Rialma is located across the Rio das Almas from Ceres on the important interstate highway BR-153, which links Anápolis to Belém. It was created as part of the urban area of Ceres, which was also created as the Colônia Nacional Agrícola de Goiás. It is part of the Ceres Microregion.
The climate is moist tropical. The most important river is the Rio das Almas, which has its source near Cocalzinho de Goiás and flows north to enter the massive Serra da Mesa reservoir, which dams up the Maranhão River.