The National Historical Geographic Information System (NHGIS) provides population, housing, agricultural, and economic data, along with GIS-compatible boundary files, for geographic units in the United States from 1790 to the present. IPUMS stands for data integrated across time, space and scientific domains. IPUMS makes it easy to study change and conduct comparative research--by imposing consistent codes, supplying detailed documentation, and creating customized datasets. Data and services are available free of charge.  Read More