Assessing and Enhancing Green Quantity in the Open Spaces of High-Density Cities: A Comparative Study of the Macau Peninsula and Monaco

Abstract

Green open space in high-density cities has positive significance in terms of improving the quality of the living environment and solving problems such as “urban diseases”. Taking the high-density urban districts of the Macau Peninsula and Monaco as examples, this study divides the planning index of open space green quantity into two dimensions: the blue-green spaces occupancy rate (BGOR) within urban land areas and the blue-green spaces visibility rate (BGVR) of the main streetscape. Using satellite remote-sensing maps, GIS databases, and street-view images, this study evaluates the current green quantity in both regions and compares them to identify best practices. This study aims to assess and enhance the green quantity found in the open spaces of high-density cities, using the Macau Peninsula and Monaco as case studies. The primary research questions are as follows: (1) How can the green quantity in open spaces be effectively measured in high-density urban environments? (2) What planning strategies can be implemented to increase the green quantity and improve the urban living environment in such areas? Therefore, this study proposes planning strategies such as three-dimensional greening, converting grey spaces to green spaces, and implementing policies to encourage public participation in greening efforts. These strategies aim to enhance the green quantity in open spaces, thereby improving the urban living environment in high-density cities like Macau and providing a reference for similar urban areas in the world.

1. Introduction

1.1. Research Background

Open space is an important part of urban land use and provides a necessary place for residents to carry out outdoor recreational and leisure activities in their daily lives [1,2,3]. Macau mainly relies on land reclamation to expand the available land. The total area has been continuously expanded due to coastal reclamation [4,5] and has gradually expanded from 11.6 square kilometers in 1912 to 29.9 km² in 2011. As of 2023, Macau’s total land area had reached 33.3 km². However, this city accommodates 686,600 people (data as of the third quarter of 2024) [6]. Population density has been increasing. For a high-density city like Macau, how do you enhance the naturalization of urban space under conditions of extremely tight land resource availability? This also brings new challenges and novel approaches to the current urban planning and design industry.

In February 2022, the Macau Special Administrative Region Government approved the implementation of the first-ever “Macau Urban Master Plan (2020–2040)”, which puts forward “the goal of Macau’s urban development and construction as a green, livable, and touristic green, low-carbon, and sustainable city” [7]. It is necessary to form an organically connected blue-green network through the planning of ecological reserves, green areas, or public open spaces, and to link green areas and water nodes such as mountains, water bodies, and parks. Based on Macau’s current situation, to achieve this planning goal, it is necessary to significantly increase the level of green space in open spaces in high-density urban areas to realize green development.

1.2. Literature Review: An Evaluation of the Amount of Green Space in International Urban Open Spaces

1.2.1. Indicators for Evaluating Green Space in the Urban Open Space Plan

In addition to the indicators “Green Area Rate” and “Green Coverage”, which are commonly used in Chinese domestic technical specifications, other indicators for evaluating the amount of green space in the plane of urban open space mainly include “Green Performance” and “Green Patch Density” [8]. Levant et al. used the green performance evaluation index to make a comprehensive evaluation of green open space in 24 European cities [9]. This index mainly calculates the proportion of green space in urban areas, the proportion of green space per 1000 residents, the existence and planning of regional green space systems, urban green space investment funds, the number of urban green open spaces, green space accessibility, and other influencing factors used in the green performance index to make a comprehensive evaluation of the quality of green open space in urban layout [3,10]. Xiao Xi et al. proposed the evaluation index of “green patch density” for high-density cities, i.e., by mapping the ratio of urban green space surrounding the boundary in satellite remote-sensing images to the total area of the city, combined with influencing factors such as the perimeter of the green space boundary, observing the density of green patches in the urban planar layout, and then evaluating the level of quantity of greenery of the spatial planar green space in high-density cities [11,12,13,14]. The level of green space in high-density urban spaces can be evaluated by observing the density of green patches in the urban layout [11,12].

1.2.2. Indicators for Evaluating the Quantity of Greenery in Urban Open Space Façades

Among the evaluation indicators related to the amount of greening of urban open space façades, the most widely used ones are the visible green index and the green view index. These two indexes, both of which essentially reflect an evaluation of the degree of greening of urban space from the visual point of view of human beings, have gradually become the new indexes for measuring the amount of greening of urban space in recent years.

Andrew Larkin et al. used the concept of the “green landscape index” to measure the greenness of urban streetscapes. The specific operation was to use an AI intelligent algorithm model for a large number of low-density residential neighborhoods to calculate, from a Google panoramic image, the green elements in proportion to the green façade, and then make a comprehensive evaluation of the green visibility of the streetscape [15]. The results of the study show that the AI machine intelligence’s computing function has great potential for development and can now be applied to evaluate the green view index of low-density neighborhoods with a relatively simple streetscape element, but the application in more complex neighborhood environments in high-density urban areas is still difficult. Huai Zhen et al., by letting a large number of experimenters watch a panoramic image of green space in urban settlements while wearing a brainwave-measuring instrument, recorded the magnitude of the brainwave changes in each experimenter’s brainwave and concluded that a green visibility rate of the panoramic picture in a value interval of 60–80% was the ideal urban living environment conditions measured by the human brain wave; at the same time, they proposed that the green space of the settlements, in the context of guaranteeing the health benefits of a residence, should be 60% [16]. According to Yoji Aoki, a well-known Japanese scholar, the “Visible Green Index” is a useful metric for gauging urban residents’ subjective psychological perceptions of the amount of green space in their city [17]. Referring to Natsuki Ogihara’s segmented evaluation method of green visibility and the documents of the Japanese Regional Urban Development Bureau and the Ministry of Land, Infrastructure, Transport, and Tourism, when the green visibility rate of urban streetscapes is more than 25%, it reaches an excellent level for the greenness of urban space façades and can be used as the target value of greenness in the planning of the façades of most urban open spaces [18].

1.3. Problem Statement and Objectives

Despite the rich body of research on green area rate, green coverage, green performance, and green patch density, there are significant gaps when applying these findings to high-density cities like Macau. Moreover, the existing literature primarily focuses on two-dimensional assessments of green space quantity, such as the proportion of green space within urban areas and the density of green patches in the urban layout. However, in high-density urban environments, it is equally important to consider the vertical dimension of green space, which is often overlooked. The visual impact of greenery from a street-level perspective, as measured by indicators like the visible green index and the green view index, has gained attention in recent years but is still underutilized in planning practices, especially in complex urban settings like Macau.

Due to the special history of the city and the current governance system of “one country, two systems” [19,20], it is difficult for Macau to copy the practices of Chinese mainland cities in terms of urban planning and construction, and often Macau must learn from the comparative experiences of international cities when formulating its development strategies. At present, there is still no research on a planning strategy for evaluating and enhancing the amount of green space in open spaces in Macau. Referring to the current national standards of Chinese domestic cities, such as the Urban Green Space Design Code (GB50420-2007) and Urban Green Space Planning Standards (GB/T51346-2019), the most commonly used indicators for urban green space evaluation and planning include the green space rate, green coverage rate, coverage rate of the service radius of parks and green spaces, the index of parks available to by 10,000 people per capita area of scenic green space in the urban area, etc. [21,22]. However, due to Macau’s special urban conditions, it is not possible to assess and improve the current green space planning strategies in Macau. Besides, due to Macau’s special municipal conditions, most of these indicators are not applicable and other indicators must be found.

This paper takes the high-density urban areas of the Macau Peninsula and the Principality of Monaco as examples and sets the planning indicators of open space green quantity into two dimensions: the blue-green spaces occupancy rate within urban land and the blue-green spaces visibility rate of the main streetscape; then, it proposes suitable indicators for Macau through an assessment of the current situation and international comparisons. This study also presents a suitable planning strategy for the enhancement of green space in urban open spaces in Macau, so as to provide a reference for the optimization of the human environment in Macau and similar high-density urban areas in China.

2. Study Area and Methods

2.1. Study Area

2.1.1. Macau Special Administrative Region in China

Macau is a port city on the coast of the Pacific Ocean and the South China Sea. It is located on the west bank of the Pearl River Estuary and at a low latitude south of the Tropic of Cancer. It is connected to Gongbei, Zhuhai, Guangdong in the north, Wan Chai and Hengqin across the tributaries of the Xijiang River, the Inner Harbor and the Jiamakou Channel to the west, Lantau Island in Hong Kong to the east across the Lingding Ocean, and the Wanshan Islands to the south [23,24,25]. The components of Macau include the Macau Peninsula in the north and the outlying islands in the south. The offshore area of Macau refers to the large island, consisting of Taipa, Coloane, and Cotai City [26]. Originally comprising Taipa Island and Coloane Island, after the construction of the Cotai Connecting Highway, reclamation and water flow from the West River brought a large amount of silt, the seabed between the two islands became shallower, and more and more land was formed along the highway. Therefore, the local government started planning for reclamation, and the resulting land became Cotai City (Figure 1), with a total area of about 32.9 km². In 2020, the population density of Macau’s urban area was about 20,800 people/km², which is one of the highest in the world [27]. Among these areas, the urban area of the Macau Peninsula is only 9.3 km², and the population density is about 58,300 people/km², representing one of the most densely populated cities in the world.

2.1.2. The Principality of Monaco

The Principality of Monaco is located in the south of France. Except for its southern coastline close to the Mediterranean Sea, the entire territory is surrounded by France on three sides to the north, west, and east [28,29]. It is mainly composed of the old city of Monaco and the surrounding areas that were subsequently established, with a land area of about 2.1 km² (Figure 2). Monaco had a resident population of about 38,000 in 2019 and a population density of about 18,413/km² [28], making it a high-density city. Monaco is a typical “city-state”, with a GDP per capita of about USD 170,000 in 2020, ranking it first in the world [30]. Monaco is currently organized into 10 urban districts, 9 administrative districts, and 1 parish. Like Macau, Monaco is one of the few high-density cities in the world with a 100% urbanization level [31]. The problems in the two cities are the same because of the small urban land area and high urban density, and both cities have no surplus land available for the construction of green spaces. In terms of the evolution of the urban form, the size and shape of Monaco’s urban area are very similar to those of the Macau Peninsula before reclamation. Except for the newly reclaimed area, the size of Monaco’s urban zoning is also similar to that of Macau’s, and the scale of the streets is even more similar to that of the streets in the urban area of the Macau Peninsula, which are all characterized by narrow and confined urban spaces. Streets in Monaco’s urban areas are mostly one-lane streets with narrow sidewalks that allow only two people to pass sideways; it is only in the newly reclaimed areas that there are more than four lanes in each direction of modern urban traffic. In terms of urban layout, history, and culture, the historic buildings in the urban areas of Monaco and the Macau Peninsula are typically European in style; the establishment of districts in Monaco and the delineation of parishes in Macau are both influenced by the Catholic culture, with churches set up in each district and parish and Catholicism as one of the main religions in the city. In terms of the city’s economy and industries, Monaco’s mainstay, like Macau’s, is tourism and gaming. Monaco and Macau are both developed economies and independent customs territories, and both rank in the top three in the 2019 Global Country/Region GDP per capita rankings. Therefore, Monaco and Macau are highly comparable when examined in terms of urban form, development status, city layout, industrial economy, and standard of living. In particular, most of the zoning areas of the Macau Peninsula are close to those of Monaco, which are both small-scale urban zones. With the exception of some zoning districts where the density of buildings is extremely high, the density of buildings in the urban area of the Macau Peninsula is basically comparable to that of Monaco. In this way, these two specific cities have high comparability. This comparability allows for a more targeted and effective analysis of urban planning strategies, especially in terms of the level of greenery enhancement in high-density urban areas.

2.2. Data Sources and Methodology

The data used in this paper included the 0.6 m accuracy satellite remote-sensing map of the whole area of Macau (October 2020 version), the 1:10,000 base map of the current status of Macau’s urban green space (2020 version), and the 1:1000 AutoCAD map of the whole area of Macau (October 2020 version), as provided by the Macau Cadastral Bureau and the Greening Department of the Municipal Services Department. Other land data and population data were drawn from References [32,33,34,35,36,37,38,39], as a supplement to the above. The study area is 9.3 km² of the urban area of the Macau Peninsula (excluding New Town Area A and the artificial island of the Hong Kong-Zhuhai-Macau Bridge, which are under construction by reclamation). Using the 1:1000 AutoCAD map of the whole area of Macau and the 0.6 m precision satellite remote-sensing map, the 1:10,000 base map of the current status of urban green space on the Macau Peninsula in 2020 was checked and updated. After topological proofreading, the green and open spatial data information of the Macau Peninsula, including the urban green space and the natural water bodies, was entered into the ArcGIS geospatial database. Subsequently, after the urban green space information of Macau was counted in the form of a GIS geospatial database, ArcGIS 10.7 software was further used to analyze and evaluate the green open space of the urban area of the Macau Peninsula (Figure 3). The research content is embodied in a set of spatial green quantity evaluation indexes: the blue-green spaces occupancy rate within urban land (BGOR), and the blue-green spaces visibility rate of the main streetscape (BGVR). The specific calculation expression is as follows:

BGOR = (GA + NW)/MS × 100%

(1)

where GA is the area of urban green space in the planning area, NW is the area of natural water bodies in the planning area, and MS is the area of urban land. The calculation of the BGOR value for each sub-area of the Macau Peninsula can be quantified by the Macau GIS green open space database:

BGVR = (EA + EW)/ES × 100%

(2)

where EA is the visible area of vegetation in the streetscape image, EW is the visible area of natural water bodies in the streetscape image, and ES is the area of the streetscape image’s view. The BGVR value is calculated by capturing the city streetscape samples from Baidu/Google Street View maps and entering them into the ArcGIS software for calculation.

The Principality of Monaco currently has eight urban administrative divisions: Fontvieille, Jardin Exotique, Monaco-Ville, La Condamine, Les Moneghetti, Larvotto, Monte-Carlo, La Rousse, and Sainte-Dévote, excluding the new district of Le Portier, which is under construction on reclaimed land. In addition, the study of the statistical area of the Fontvieille and La Condamine districts in Monaco’s urban subdistricts includes the natural waters of the two inner city harbors, Port de Fontvieille and Port Hercule de Monaco, respectively (Figure 4).

Population data for Monaco’s city subdivisions were taken from the 2016 census of the Principality of Monaco. Of these, no permanent population counts are available for Sainte-Dévote. The data sources underlying the BGOR values for the study of Monaco’s nine city sub-districts include Open Street Map 50-meter-accuracy multi-layer vector map data (2021 edition), Google Earth satellite image maps with a maximum accuracy of 7.0 m (2018 edition), Monaco city statistics, and Monaco’s 2016 city sub-district population census data. The method used for Monaco city map GIS data analysis is to extract the 50-meter-precision Open Street Map urban green open space-related layers and convert them into isometric vectorized map data by scale. Then, the map information data are imported into the ArcGIS spatial database. On this basis, the map information data analysis and statistics function of ArcGIS 10.7 software is used to extract the map information related to green open spaces in the Monaco urban zoning area, further analyze the proportion of green open space in Monaco city, and conduct a comparative analysis with the urban area of the Macau Peninsula.

Regarding indicators for evaluating the amount of green in the three-dimensional urban façade landscape, the visible green index, i.e., the percentage of green in one’s field of vision, is researched more frequently in the academic world at present. In Japan, the green visibility index has been officially used to evaluate the greening level of urban neighborhoods. However, in a waterfront city, the natural elements in the streetscape space are not only green but also include the blue color of the water area. Therefore, this paper proposes to use the BGVR as an indicator for examining the level of naturalization of urban spaces. Referring to the calculation method for the stratified sampling of the green visibility rate, and taking into account the actual situation in Macau, the specific measurement method of BGVR is as follows:

(1)

Select six streets with representative landscapes in each of the 17 sub-districts of the Macau Peninsula, with names such as Avenida de, Avenida, Avenue, Largo, and so on. Then, we take one node landscape in each street for measurement purposes; the location of the selected points is shown in Figure 5.

(2)

Use the Baidu map website’s 2019–2020 version of the street view image as a sampling base map, framing the camera installed in the street view, shooting from a car roof at a height of about 2.5 m above the ground, with the lens position along the street center line perspective shift, and framing a time period for sufficient daylight between 8:00 a.m. and 17:00 p.m.

(3)

Using ArcMap 10.7 software, the blue and green natural elements in each streetscape image are labeled with blue and green layers, in combination with the semantic segmentation method. The percentage of each blue and green natural spatial element’s labeled layer in the streetscape map is calculated one by one. Lastly, the percentage of blue-green layers in each streetscape image in ArcMap is converted isometrically to the BVGR values for streetscape nodes in each neighborhood for statistical purposes (for example, the Barra e Manduco district, Tamagnini Barbosa district, and Guia district).

3. Results

3.1. Evaluation of the Quantity of Green Areas in the Macau Peninsula

3.1.1. Evaluation of Open Space and Green Quantity in the Urban Areas of the Macau Peninsula

By the end of 2020, the area of urban green space on the Macau Peninsula was 1,817,215 m², the area of natural water bodies was 550,501 m², and the BGOR rate was 24.8%. Through further study of the 17 sub-districts of the Macau Peninsula, it was found that the gap between the green open space indicators of each sub-district was obvious. For example, the difference between the indicators of the Barca and Guia districts was more than 65%, and the polarization of the urban environment was more marked.

As shown in Figure 3 and

Table 1. Summary of BGOR volume calculations for 17 sub-districts in the Macau Peninsula.

No.	City Zoning and Numbering	BGOR (%)	No.	City Zoning and Numbering	BGOR (%)
17	9. Barca	0.91	8	10. Patane e São Paulo	13.60
16	8. Horta e Costa e Ouvidor Arriaga	2.58	7	4. NATAP	14.09
15	7. Doca do Lamau	5.34	6	13. ZAPE	14.47
14	16. Barra e Manduco	6.61	5	2. Tamagnini Barbosa	18.72
13	15. Baixa de Macau	7.70	4	17. Praia Grande e Penha	25.00
12	3. Areia Preta e Iao Hon	7.74	3	14. NAPE e Aterros da Baía da Praia Grande	42.82
11	6. Fai Chi Kei	10.11	2	5. Móng Há e Reservatório	52.95
10	11. Conselheiro Ferreira de Almeida	11.27	1	12. Guia	67.49
9	1. Ilha Verde	12.84	Area-wide average	Macau Peninsula	24.80

Source: statistics and plotting by the author.

, the average value of BGOR for the 17 urban areas in the Macau Peninsula urban area is 18.5%, and there are large gaps among the indicators between the sub-districts. Among them, the north-central regions of the peninsula (the Barca district and Horta e Costa e Ouvidor Arriaga district) have the lowest BGOR values, which are 0.91% and 2.58%, respectively. The central, western, and part of the northern regions (Baixa de Macau district, Doca do Lamau district, Fai Chi Kei district, Areia Preta e Iao Hon districts, Barra e Manduco district, etc.) have a BGOR value of less than 10%; the southeastern, northeastern, and part of the northwestern regions (ZAPE district, NATAP district, and Ilha Verde district) BGOR values are moderate, ranging from 10% to 15%. The southwest and southern regions (Praia Grande e Penha district and NAPE e Aterros da Baía da Praia Grande district) have high levels of BGOR values, ranging from 25% to 43%, and the eastern region (Móng Há e Reservatório district and Guia district) had the highest levels of BGOR values, at 52.95% and 67.49%, respectively.

3.1.2. Evaluation of the Green Quantity of Open Space Façades in the Urban Areas of the Macau Peninsula

Evaluations were made by combining an analysis of the BGVR indicator of the major streetscape in the neighborhoods of the Macau Peninsula in Table 1 above and referring to the segmented evaluation method of green visibility rate proposed by the Japanese scholar Natsuki Ogihara. The BGVR indicators of Macau’s various neighborhoods can be roughly categorized into three intervals: lower (<15%), medium (15~25%), and higher (>25%), with an average of 18.3% for the whole area of the Macau Peninsula, which is at the medium level. As can be seen from

Table 2. The Macau Peninsula’s 17 sub-district BGVR values, showing measurement illustrations.

Barra e Manduco BGVR Average = 7.6%
(1) Avenida de Sai Van BGVR = 19.7%	(2) Rua do Almirante Sérgio BGVR = 5.9%	(3) Rua da Praia do Manduco BGVR = 2.0%
(4) Travessa De Chan Loc BGVR = 11.3%	(5) Rua Dos Cules BGVR = 1.2%	(6) Rua das Lorchas BGVR = 5.2%
Tamagnini Barbosa BGVR Average =13.9%
(1) Avenida do Conselheiro BGVR = 15.9%	(2) Rua Central de Toi Sán BGVR = 18.4%	(3) Avenida de la Barbosa BGVR = 33.3%
(4) Rua Marginal do Canal das Hortas BGVR = 1.9%	(5) Praça das Portas do Cerco BGVR = 8.1%	(6) Rua Vá Tai BGVR = 5.8%
Guia BGVR Average =23.8%
(1) Avenida de Sidónio Pais BGVR = 31.3%	(2) Estrada Do Engenheiro Trigo BGVR = 47.9%	(3) Estrada da Vitória BGVR = 18.3%
(4) Rua da Fonte da Inveja BGVR = 16.8%	(5) Estrada de Cacilhas BGVR = 12.6%	(6) Calçada Da Vitória BGVR = 15.8%

Source: statistics and plotting by the author.

and

Table 3. Sorting of BGVR values in 17 sub-districts of the Macau Peninsula.

No.	City Zoning and Numbering	BGOR (%)	No.	City Zoning and Numbering	BGOR (%)
17	10. Patane e São Paulo	6.7	8	7. Doca do Lamau	17.9
16	16. Barra e Manduco	7.6	7	14. NAPE e Aterros da Baía da Praia Grande	23.0
15	9. Barca	9.8	6	5. Móng Há e Reservatório	23.0
14	6. Fai Chi Kei	13.8	5	12. Guia	23.8
13	2. Tamagnini Barbosa	13.9	4	13. ZAPE	24.1
12	3. Areia Preta e Iao Hon	14.8	3	1. Ilha Verde	24.7
11	11. Conselheiro Ferreira de Almeida	15.0	2	4. NATAP	26.5
10	8. Horta e Costa e Ouvidor Arriaga	16.8	1	17. Praia Grande e Penha	33.3
9	15. Baixa de Macau	16.9	Area-wide average	Macau Peninsula	Average 18.3

Source: statistics and plotting by the author.

, the distribution of BGVR values in the neighborhoods of the Macau Peninsula is uneven, with higher BGVR values seen mainly in the new reclamation areas, such as the NATAP district, NAPE e Aterros da Baía da Praia Grande district, and ZAPE district. In contrast, the core, old districts of the Peninsula (e.g., Barra e Manduco district, Barca district, and Patane e São Paulo districts) have single-digit BGVR values, indicating a poor level. Overall, among the 17 sub-districts of the Macau Peninsula, there are 6 urban areas with poor BGVR values, 9 urban areas with moderate values, and only 2 urban areas with better values.

3.2. Empirical Comparison: Evaluation of the Green Quantity of Urban Open Spaces in Monaco

3.2.1. Evaluation of the Greening of Monaco’s Urban Open Space Plan

As previously mentioned in the methodology, the researchers utilized ArcGIS 10.7 software for mapping, data analysis, and statistics to extract pertinent information about green open spaces in Monaco’s urban districts. They then further analyzed the proportion of green open spaces in Monaco (

Table 4. Measurement of BGOR in Monaco, shown by sub-district.

City Zoning and Numbering	City Zoning Area (m2)	Area of Green Open Space in the Sub-District (m2)	Urban Population (People)	Area of Green Open Space per Capita (People/m2)	BGOR (%)
1. Fontvieille	392,930	125,345	4420	23.8	31.9
2. Jardin Exotique	240,000	41,280	5117	8.1	17.2
3. Monaco-Ville	200,000	45,600	1064	42.9	22.8
4. La Condamine	536,550	260,227	5141	28.3	48.5
5. Les Moneghetti	120,000	87	4195	0.02	0
6. Sainte-Dévote	20,000	2480	-	-	12.4
7. Monte-Carlo	440,000	38,720	8259	4.7	8.8
8. Larvotto	220,000	30,800	2026	15.2	14.0
9. La Rousse	180,000	7020	7087	1.0	3.9
Total	2,349,480	551,559	37,309	Average 14.8	Area-wide average 23.5

Source: statistics and plotting by the author.

) and subsequently compared and analyzed it with the urban areas of the Macau Peninsula (

Table 5. Comparison of BGOR values between Monaco and the Macau Peninsula, shown by sub-district.

Subdivision of the City of Monaco	BGOR (%)	Macau Peninsula Urban Zoning	BGOR (%)	Macau Peninsula Urban Zoning	BGOR (%)
1. Fontvieille	31.9	1. Ilha Verde	12.84	10. Patane e São Paulo	13.60
2. Jardin Exotique	17.2	2. Tamagnini Barbosa	18.72	11. Conselheiro Ferreira de Almeida	11.27
3. Monaco-Ville	22.8	3. Areia Preta e Iao Hon	7.74	12. Guia	67.49
4. La Condamine	48.5	4. NATAP	14.09	13. ZAPE	14.47
5. Les Moneghetti	0	5. Móng Há e Reservatório	52.95	14. NAPE e Aterros da Baía da Praia Grande	42.82
6. Sainte-Dévote	12.4	6. Fai Chi Kei	10.11	15. Baixa de Macau	7.70
7. Monte-Carlo	8.8	7. Doca do Lamau	5.34	16. Barra e Manduco	6.61
8. Larvotto	14.0	8. Horta e Costa e Ouvidor Arriaga	2.58	17. Praia Grande e Penha	25.00
9. La Rousse	3.9	9. Barca	0.91

Source: statistics and plotting by the author.

and

Table 6. Comparison of urban green space per capita between Monaco and the Macau Peninsula, shown by sub-district.

Subdivision of the City of Monaco	Urban Green Space per Capita (m²)	Macau Peninsula Urban Zoning	Urban Green Space per Capita (m²)	Macau Peninsula Urban Zoning	Urban Green Space per Capita (m²)
1. Fontvieille	23.8	1. Ilha Verde	2.49	10. Patane e São Paulo	13.60
2. Jardin Exotique	8.1	2. Tamagnini Barbosa	2.06	11. Conselheiro Ferreira de Almeida	11.27
3. Monaco-Ville	42.9	3. Areia Preta e Iao Hon	0.45	12. Guia	67.49
4. La Condamine	28.3	4. NATAP	1.19	13. ZAPE	14.47
5. Les Moneghetti	0.02	5.Móng Há e Reservatório	19.25	14. NAPE e Aterros da Baía da Praia Grande	32.98
6. Sainte-Dévote	-	6. Fai Chi Kei	1.07	15. Baixa de Macau	7.70
7. Monte-Carlo	4.7	7. Doca do Lamau	0.35	16. Barra e Manduco	6.61
8. Larvotto	15.2	8. Horta e Costa e Ouvidor Arriaga	0.19	17. Praia Grande e Penha	25.00
9. La Rousse	1.0	9. Barca	0.06

Source: statistics and plotting by the author.

). The specific results are shown below.

The research data show that the current BGOR value of Monaco is 23.5%, which is closer to the BGOR value of 24.8% for the urban area of the Macau Peninsula. In particular, the per capita green open space area of Monaco’s 8 urban administrative sub-districts is close to the per capita value of the 17 sub-districts on the Macau Peninsula. Some urban districts in Monaco (e.g., Monte-Carlo District and Jardin Exotique District) have similar land-use conditions as Ilha Verde District and Baixa de Macau District on the Macau Peninsula, with lower urban green space occupancy, all having single-digit BGOR values, and urban districts that are extremely lacking in green space. At the same time, both Monaco and the Macau Peninsula also have several urban areas with high urban green space occupancy rates and BGOR values greater than 20%, which support the beautiful landscape of the coastal tourist cities, such as Monaco’s Fontvieille district, the Monaco-Ville district, and the Macau Peninsula’s Praia Grande e Penha district and NAPE e Aterros da Baía da Praia Grande district.

3.2.2. Evaluation of the Green Quantity of Open Space Façades in the Urban Area of Monaco

This research on the BGVR value of Monaco is consistent with the above research method regarding the neighborhood landscape of Macau. The sampling and quantification research process is as follows:

(1)

According to the size of the area of different sub-districts and the number of roads in Monaco, three to six main streets with representative landscapes are selected in each city sub-district for quantification of the BGVR value, including Boulevard, Avenue, Rue, and Quai, using different scales of streets, with each street a node streetscape. Among them, the streets of Boulevard, Avenue, Rue, Quai and others correspond to streets on the same scale in Macau, such as Avenida, Estrada, Rua, Travessa, and so on.

(2)

Using the Google Maps Street View image, version 2020–2021, as the sampling base map, the BGVR values of the main streetscapes in each city sub-division of Monaco are calculated (

Table 7. Example of the calculation of BGVR values for the Monaco districts of Larvotto and La Rousse.

Larvotto BGVR average value = 32.6%
(1) Princess Grace Boulevard BGVR = 29.4%	(2) Larvotto Boulevard BGVR = 35.4%	(3) Princess Grace Street BGVR = 33.1%
La Rousse BGVR average value = 39.1%
(4) Father Luis Flora Street BGVR = 44.0%	(5) Turnau Avenue BGVR = 38.9%	(6) Via Italia BGVR = 34.5%

Source: statistics and plotting by the author.

).

(3)

The blue and green natural elements of the street scene images of each city sub-district of Monaco were identified with blue and green layers, using ArcMap 10.7 software, and the percentage of each blue and green natural spatial element identification layer in each street scene map surface was calculated one by one. Then, the blue and green layer percentage of the street scene images was converted isometrically to BVGR values for the nodes of each neighborhood of Monaco using ArcMap software for analysis (

Table 8. Comparison of BGVR values between the urban zones of Monaco and the Macau Peninsula.

Subdivision of the City of Monaco	BGVR (%)	Macau Peninsula Urban Zoning	BGVR (%)	Macau Peninsula Urban Zoning	BGVR (%)
1. Fontvieille	33.1	1. Ilha Verde	24.7	10. Patane e São Paulo	6.7
2. Jardin Exotique	31.5	2. Tamagnini Barbosa	13.9	11. Conselheiro Ferreira de Almeida	15.0
3. Monaco-Ville	65.7	3. Areia Preta e Iao Hon	14.8	12. Guia	23.8
4. La Condamine	17.2	4. NATAP	26.5	13. ZAPE	24.1
5. Les Moneghetti	17.9	5.Móng Há e Reservatório	23.0	14. NAPE e Aterros da Baía da Praia Grande	23.0
6. Sainte-Dévote	18.5	6. Fai Chi Kei	13.8	15. Baixa de Macau	16.9
7. Monte-Carlo	23.5	7. Doca do Lamau	17.9	16. Barra e Manduco	7.6
8. Larvotto	32.6	8. Horta e Costa e Ouvidor Arriaga	16.8	17. Praia Grande e Penha	33.3
9. La Rousse	39.1	9. Barca	9.8
Monaco-wide	Average 31.0			Macau Peninsula-wide	Average 18.3

Source: statistics and plotting by the author.

).

The research showed that although the BGOR values of the urban subzones of Monaco and the Macau Peninsula are comparable, the BGVR values are different. According to the three intervals categorized by the BGVR indicator above, Monaco has no subzones with low BGVR values (<15%) and three subzones with medium levels (15–25%), accounting for 33.3% of the total, with the remaining six subzones with high levels (>25%) accounting for 66.6% of the total (

Table 9. Summary of information related to green open space in each of Monaco’s municipal subdivisions.

City Zoning and Numbering	Area of Zoning (m²)	Area of Urban Green Open Space (m²)	Urban Population (People)	Area of Green Open Space per Capita (m²/People)	BGVR (%)	BGOR (%)
1. Fontvieille	392,930	125,345	4420	23.8	33.1	31.9
2. Jardin Exotique	240,000	41,280	5117	8.1	31.5	17.2
3. Monaco-Ville	200,000	45,600	1064	42.9	65.7	22.8
4. La Condamine	536,550	260,227	5141	28.3	17.2	48.5
5. Les Moneghetti	120,000	87	4195	0.02	17.9	0
6. Sainte-Dévote	20,000	2480	-	-	18.5	12.4
7. Monte-Carlo	440,000	38,720	8259	4.7	23.5	8.8
8. Larvotto	220,000	30,800	2026	15.2	32.6	14.0
9. La Rousse	180,000	7020	7087	1.0	39.1	3.9
Total	2,349,480	551,559	37,308	Area-wide average 14.8	Average 31.0	Area-wide average 23.5

Source: statistics and plotting by the author.

). The average BGVR value for the whole area of Monaco was 31.0%, which was 12.7% higher than that of 18.3% for the Macau Peninsula, indicating that the naturalized landscape of the façade space in the urban area of Monaco was better and substantially higher than that of the urban area of the Macau Peninsula. If we compare the extreme values of BGOR between the Monaco and Macau Peninsula urban sub-districts, for example, the Les Moneghetti district in Monaco can still achieve a BGVR value of 17.9% for its façade space, although its BGOR value is about 0 and its per capita area of green open space is 0.02 m². Comparatively speaking, the BGVR value of the Barca district on the Macau Peninsula, which has a BGOR value of 0.91, is only 9.8, which is substantially lower than that of the Les Moneghetti district. It can be seen that by strengthening the three-dimensional greening of neighborhoods, the level of spatial greening in high-density urban areas can be effectively improved and the level of spatial naturalization enhanced.

4. Discussion: Planning Strategies for Enhancing Green Space in Open Space on the Macau Peninsula

4.1. Strategies for Enhancing the Quantity of Greenery of Land Use Plans

Unlike the public ownership of land in Chinese mainland cities, the Basic Law of the Macau Special Administrative Region of the People’s Republic of China (Lei Básica da Região Administrativa Especial de Macau da República Popular da China) explicitly protects private land and property, and the government does not have the right to build on or remodel privately owned land or properties other than those owned by the government. Therefore, the protection system of land property rights stipulated in the Basic Law of the Macau Special Administrative Region of the People’s Republic of China is one of the main factors affecting the difficult operation of Macau’s urban master plan and the preparation of plans related to land use in recent years.

The population data of Macau in the past 20 years show that the number of people in Macau has been increasing year by year, and the density of the urban population has also been increasing (

Table 10. Population statistics of the Macau Special Administrative Region from 2004 to 2024.

Year	Total Population of Macau
2004	465,333
2005	488,144
2006	512,423
2007	538,100
2008	549,200
2009	542,200
2010	552,300
2011	557,400
2012	582,000
2013	607,500
2014	636,200
2015	646,800
2016	644,900
2017	653,100
2018	667,400
2019	679,600
2020	683,100
2021	683,200
2022	672,800
2023	683,700
2024	686,600

Source: statistics data from the Government of Macau Special Administrative Region Statistics and Census Service. The deadline for Macau’s demographic statistics in 2024 is the third quarter of 2024.

). The population data for Macau in the past 20 years can be used to project that the population of Macau will continue to show an increasing trend in the next 10 years. This means that an increasing urban population needs to be accommodated in the already limited urban green space, resulting in a serious shortage of urban green space per capita. Regarding the current situation of green open space in the urban areas of the Macau Peninsula, some have suggested that residents should be allowed to “see the green seams and build micro-green spaces” within the streets to increase the amount of green space, but the relevant measures can only be implemented with the cooperation of the citizens on their own initiative and on the premise of complying with the Basic Law of Macau. Although the method of “plugging in the green seams” has had some effect on the greening rate of some neighborhoods, it is not enough to substantially solve the actual problems of the Macau Peninsula, such as the low per capita green space rate. Therefore, for the Macau Peninsula, the way to improve the quality of the human environment in high-density urban areas would be to change the nature of the use of some government-controlled land and to adjust the attributes of some urban land through scientific planning.

Among the 18 sub-categories of Macau’s current urban green space classification, only 13 are mainly under the management of the Macau Municipal Affairs Bureau, and the rest are mostly privately owned. In the urban area of the Peninsula, managed by the Macau Municipal Affairs Bureau, there is also a large area of urban squares and foregrounds belonging to the “gray open space” category that can be changed in terms of the nature of the land. The degree of greening of these sites is generally low, with a green area ratio of less than 30%, making it impossible to include them in the category of urban green space. They can be upgraded through measures such as expanding the area of green pavement and planting trees to increase the amount of green space, so that they can then be transformed into urban green spaces.

As shown in

Table 11. Comparison of before and after BGOR value enhancement in 17 sub-districts of the Macau Peninsula.

Macau Peninsula Urban Zoning	Urban Area (km2)	Gray Open Space Area Available (m2)	Current Urban Zoning BGOR Values (%)	Upgraded Urban Zoning BGOR (%)
1. Ilha Verde	0.5	3230	12.84	13.49
2. Tamagnini Barbosa	0.4	4216	18.72	19.77
3. Areia Preta e Iao Hon	0.4	797	7.74	7.94
4. NATAP	0.6	639	14.09	14.20
5. Móng Há e Reservatório	1.0	0	52.95	-
6. Fai Chi Kei	0.3	3846	9.90	11.18
7. Doca do Lamau	0.2	2565	5.34	6.62
8. Horta e Costa e Ouvidor Arriaga	0.2	253	2.58	2.71
9. Barca	0.3	0	0.91	-
10. Patane e São Paulo	0.4	4911	13.60	14.83
11. Conselheiro Ferreira de Almeida	0.3	743	11.27	11.52
12. Guia	0.3	0	67.49	-
13. ZAPE	0.8	97	14.47	14.48
14. NAPE e Aterros da Baía da Praia Grande	2.1	1569	42.82	42.89
15. Baixa de Macau	0.5	438	7.70	7.79
16. Barra e Manduco	0.5	306	6.61	6.67
17. Praia Grande e Penha	0.4	0	25.00	-

Source: statistics and plotting by the author.

, by calculating the potential greenable land in the Macau Peninsula, more than 10 of the 13 urban areas with a current BGOR value in the Macau Peninsula of lower than 20% can be upgraded by changing the land attributes of the urban gray open space (Open Space Reserve Land) and transforming the land attributes into green space through greening, thereby enhancing the BGOR value of the urban zoning. For example, high-density urban areas such as the Ilha Verde district, Tamagnini Barbosa district, and Patane e São Paulo district can directly increase the occupancy rate of urban green open space by more than 1%, which is of practical significance regarding the improvement of the actual quality of the human environment in the Macau Peninsula.

4.2. Strategies for Enhancing the Quantity of Greenery of Neighborhood Landscape Façades

Monaco’s experience can provide a reference for Macau’s high-density neighborhoods to enhance spatial naturalization. In terms of the planar indicator of the urban green space occupancy rate (BGOR), the urban area of Monaco is slightly lower than that of the Macau Peninsula by 1.3%. However, Monaco’s BGVR value is higher than that of the urban area of the Macau Peninsula by 12.7%, indicating the higher level of spatial naturalization of its neighborhood façade. Taking Av. Princess Grace in Monaco as an example, the improvement in BGVR is mainly due to the extensive wall greening of the building façades along the street, using trellis rails combined with climbing plants. These vertical greenings can directly increase the BGVR value of a building façade by 51.9%, and the effect on the BGVR value of the streetscape space is as high as 27.8% (Figure 6 and Figure 7), which is a valuable experience from which Macau can learn.

In some urban areas on the Macau Peninsula with low planar BGOR and façade BGVR values, the walls of buildings along the streets in many neighborhoods are not greened as a façade. Taking Rua dos Hortelãos and Avenida da Praia Grande in Areia Preta e Iao Hon district as examples, after simulating the façade area’s share of the building walls along the street and estimating the greenable space of the wall surfaces of the two streets in combination with the ArcGIS software, it was concluded that the BGVR values of the two neighborhoods could be increased by 21.5% and 28.0%, respectively (Figure 8 and Figure 9). If this wall greening is implemented, the neighborhoods with BGVR values that were originally at the poor level can be improved to a medium-high level. Therefore, in the case of urban land constraints that make it difficult to expand green space construction, the use of three-dimensional greening technology in high-density urban areas of the Macau Peninsula can effectively improve the greening level of the neighborhood’s façades, which is a greening pathway worth promoting in urban spaces.

4.3. Policies to Encourage Public Participation in Greening Strategies

Macau has a history of land reclamation to expand the available land. From 11.6 km² in 1912 to 33.3 km² as of 2023, this city has continuously expanded its land area through coastal reclamation. During this period, green space development was not a primary focus, leading to a relatively low green space ratio in the first urban areas. The early focus on land reclamation and economic development without sufficient attention being paid to green space planning has left a legacy of low green space coverage in many older urban areas. For example, the central districts of the Macau Peninsula have a green space ratio of less than 10%, with some areas having a BGOR value as low as 0.91%. In the 1990s and early 2000s, there was a gradual shift in urban planning policies toward more sustainable development. The government began to recognize the importance of green spaces for improving the inhabitants’ quality of life and started to allocate more land for parks and green areas in the newly planned urban district. However, since the high-density centralized urban area of the Macau Peninsula was already built in the 20th century, the problem of a lack of urban green space in the high-density urban areas of the Macau Peninsula has not been improved.

In high-density cities, one of the greening strategies that can directly increase the amount of greening in urban spaces is to encourage residents to green their balconies, rooftops, and patios. Currently, there are a number of internationally developed city governments that have introduced a series of economic incentive policies to encourage residents to actively participate in urban greening. For example, the Portland Municipal Government of the United States has adopted the Green Roofs policy, which requires that the green roof coverage rate of urban public facilities should reach 70%. As an incentive, developers can receive additional compensation for building plot ratios while reducing some of the stormwater management fees. Commercial and industrial buildings can be subsidized by USD 6.06 per 1000 m² [40]. Several German cities have introduced economic incentives since 1983 to continuously encourage residents to implement green roofs, green walls, and green gardens on their own initiative. The Berlin City Council, in order to increase the amount of roof-based green space in the city’s high-density neighborhoods by about 65,750 m², subsidizes the construction costs of roof greening by EUR 25–60/m² for residents of the area. The city of Linz, Austria, has introduced a comprehensive and legally binding greening policy, which stipulates that if a building of more than 100 m² with a slope of up to 20° is to be constructed in the city, 12 cm of plant growth medium must be retained on the uppermost surface of the roof structure, and more than 80% of the roof surface must be covered with vegetation. In the case of the construction of underground parking lots and other facilities, more than 30% of the roof surface of the parking lots should be retained as a greening area. In order to encourage the implementation of this statutory policy, the Municipality of Linz has implemented a policy of reimbursing up to 30% of the total cost of the construction, including the cost of construction and design, which is given to the builder as compensation [41].

In contrast, there are no economic incentives to encourage residents to actively participate in the greening of roofs, walls, balconies, and gardens in the urban planning and greening policies of the Macau SAR Government. In the high-density urban areas of the Macau Peninsula, except for some high-class neighborhoods and casinos that have roof gardens, most of the roofs of residential buildings are still in a state of “abandonment” (Figure 10). Compared with the urban governance situation in developed countries, it is not enough for the Macau SAR government to call on citizens to carry out urban greening on their own initiative through publicity. Incentive policies must be put in place to mobilize citizens and enterprises in order to promote spatial greening in the high-density urban areas of Macau.

5. Conclusions

The Macau Peninsula is a high-density international city with extremely scarce land resources. Optimizing the use of green open space resources through scientific planning to support the sustainable development of the urban environment in the future is a significant challenge. As Macau’s urban industry develops and its population continues to increase, the demand for green open spaces will also rise year by year. It is essential to think long-term and rationally plan the current urban open space resources.

For the high-density urban areas of the Macau Peninsula, the planning strategies for the enhancement of the quantity of greenery in urban open spaces mainly include:

(1) Three-dimensional greening: by all means, vigorously promote the development of three-dimensional greening of building façades and roofs in high-density neighborhoods, so as to effectively enhance the amount of green space.

(2) Turning grey into green: greening part of the existing gray open space (i.e., the current open space reserve land, such as the ungreened Largo and Plaza) and releasing about 23,000 square meters of green space in the central area of the city after reasonable greening of the Largo and Plaza.

(3) Planning for greening: 30% of the land in the new reclamation area A/C/D/E, which is being reclaimed for construction, will be planned as green space, which can increase the area by about 150 hectares of green space.

(4) Policies to pave the way for greening: formulate appropriate greening incentive policies to guide citizens toward actively participating in expanding the open space and the three-dimensional greening of Macau’s existing urban neighborhoods, and to expand the blue and green spatial vista of the waterfront shoreline. In addition, the Macau SAR government can transfer part of the permanent population and tourism and other industries to the neighboring Hengqin island in the future, so as to reduce the population density of the urban area of the Macau Peninsula and improve the per capita level of green open space.

In addition to these strategies, it is crucial to monitor and evaluate the effectiveness of these measures over time. This can be achieved through regular assessments of green space quantity and quality, as well as through feedback from the community. Public participation and education are also key components of a successful greening strategy, as they can help to foster a sense of ownership and responsibility among the residents regarding urban green spaces.

Overall, Macau is a high-density international city with extremely scarce land resources, and it is a major challenge to optimize the use of green open space background resources through scientific planning in order to support the sustainable development of the urban environment in the future. As Macau’s urban industry develops and its population continues to increase, the demand for green open space will also increase year by year, and it is necessary to think long-term and rationally plan the current urban open space resources. The greening strategy for open space in high-density urban areas of Macau that is proposed in this paper can also provide a reference for the construction of similar high-density urban centers in the world.