What are area-level data?
Area-level data describe places. These data are compiled statistics, such as number of males in a given locality. Therefore, the unit of observation is the geographic unit (e.g. state, county), and not the individual males. In TerraPop, each record in area-level data refers to a geographic unit at a given geographic level within a given country. For example, data for each state in the US. Area-level data are published by national statistical agencies and similar organizations.
In addition to aggregate population statistics compiled from censuses, information about land use, economic characteristics, health, government policies, and more may be presented as area-level data. For example, an agricultural census may have data on total crop yield by county; the World Bank maintains data on GNP by country; a disease surveillance program may provide data on the number of cases of a disease by state; and policy databases may indicate the types of deforestation policies enacted by country.
Area-level data can be easier to work with than microdata because they generally have fewer records and do not carry the same confidentiality constraints. Area-level data may also be available with finer geographic resolution than microdata. For example, the smallest geographic units identified on U.S. microdata are �public use microdata areas,� which have populations of at least 100,000, while most U.S. aggregate census data are available for census tracts, which have populations around 4,000. However, the aggregation reduces the flexibility found in microdata and therefore may not be suitable to answer all research questions.
TerraPop can derive area-level data from raster data by summarizing the values of the raster cells that fall within each geographic unit. TerraPop can also transform area-level data into raster data by distributing data about geographic units over the grid cells within each unit. Area-level data can also be attached to microdata as contextual variables describing the geographic units in which individuals and households are located.