here is some interesting information on the purpose of the National Census.
[link to www.thisnation.com
here is a small section from the website:
in addition to collecting population data for the purposes of accurately apportioning congressional districts, the federal government uses census data, among other reasons, to determine:
The allocation of federal funding for education programs in states and communities.
National social and health statistics used by a variety of agencies for policy purposes.
The allocation of federal dollars for law enforcement, federal highway projects, aid to farmers and many other federally financed activities and programs.
A wide variety of economic statistics that become the basis of the nation's economic policies.