Population is a key variable in the study of global environmental change.
Ideally, each site is studied by employing a time series of demographic data across multiple levels of spatial aggregation. At the site level, data about the population of local settlements and user groups are always collected. At regional levels, researchers make use of census data from a variety of sources such as health clinics, schools, and national government censuses, which may be aggregated by hamlets, towns, municipalities, and provinces.