Population data are primarily generated by censuses and surveys conducted by national governments. IPUMS Terra includes population data in two general forms, microdata and aggregate data.
Microdata describe the characteristics of individuals and their families and households. Each individual and household is represented as a record consisting of a number of variables describing the characteristics of the individual (e.g., age, sex, occupation, level of education, country of birth) or household (e.g., number of persons, ownership of dwelling, number of rooms, water supply). Microdata records include information about the household membership of each individual and the interrelationships among members of households.
IPUMS Terra draws on microdata made available by IPUMS International, which includes data from over 80 countries and 250 censuses dating from 1960 to 2011, with additional countries and censuses continually being processed.
Aggregate data describe the characteristics of places defined by some type of boundaries (e.g., municipalities, counties, territories, states). Aggregate population variables summarize the characteristics of people living within the boundaries, often by classifying households or individuals into categories (e.g., age ranges, income levels, number of children, industry of employment). Populations may also be grouped over two or more categories to provide more detailed information. For example, age-by-sex data might count males under age 5, males ages 5-9, males ages 10-14, etc. and females under age 5, females ages 5-9, females ages 10-14, etc. Aggregate data may also describe characteristics of whole geographic units, such as median income or total value of goods produced.
IPUMS Terra constructs aggregate data covering many topics from IPUMS-International microdata. IPUMS Terra also includes published aggregate data from the national statistical offices of over 80 countries, focusing on countries not participating in IPUMS-International.