"The National Flood Insurance Program (NFIP) was established by the National Flood Insurance Act of 1968. […] The NFIP is a program in which communities formally agree, as evidenced by their adoption of codes and ordinances, to regulate the use of their flood-prone lands. In return, FEMA [Federal Emergency Management Agency] makes flood insurance coverage available on buildings and their contents throughout the community. FEMA has traditionally identified these flood hazard areas on maps which are provided to communities for carrying out their responsibilities. The maps are also used by insurance producers to determine rates and by lenders to determine purchase requirements." This document includes revisions that take effect on October 1, 2011.
United States Federal Emergency Management Agency: http://www.fema.gov/