TIGERweb
TIGERweb is a web portal maintained by the Census Bureau for GIS access.
History
Topologically Integrated Geographic Encoding and Referencing (TIGER), sometimes known as TIGER/Lines, refers to both a GIS database and the shapefiles it contains. This information is all public domain.
TIGERweb was created as the modern interface for this data. It is the recommended tool for examining geographies available in Census Bureau datasets, such as PUMAs.