Population, or demographic data, is often included in other statistical sites. Political, health, and environmental datasets often include data about the population.
What's the difference between a Census block and tract? When should you use City boundaries and when should you use Metropolitan Statistical Area (and what's a Micropolitan Statistical Area)?
TIGER = Topologically Integrated Geographic Encoding and Referencing
TIGER/line shapefiles are the outlines of all the different legal boundaries and names used by the Census Bureau when they collect data. This includes States, Counties, Cities, Metropolitan Areas, Blocks, Tracts, and more. They also include roads, rivers, and railroads.