Agglomerations consist of contiguous built-up residential areas.
Because they do not correspond to administrative units or officially designated urban areas, agglomerations frequently cross state or province boundaries. Circles, which are identified by the latitude and longitude of their centers, are drawn with radii ranging from 0.3 to 2.0 nautical miles. The residential area of a circle is not necessarily of uniform density. The country's rural residual population is distributed in a gridwork of cells of 20 minutes of latitude by 30 minutes of longitude. Large agglomerations typically have numerous groups of circles with different rates of growth.