The U.S. Census Bureau will release the new Congressional apportionment figures at a Dec. 21 news conference at the National Press Club, making official the number of Congressional districts each state will have for the next 10 years.

The new figures will be based on the populations of each state as found in the 2010 census. Population changes affect not only the size of each state’s delegation but also its number of electoral votes.

The Census Bureau has also developed some tools to help explain the reapportionment process, including an animated video and interactive map on its website, 2010.census.gov. The map shows population changes in the states based on the 2000 census, but it will be updated Dec. 21 to illustrate the new numbers.

One trend expected to continue from the previous census is population growth rates in the South and West far outpacing those in the North and East. Ohio, Michigan, Pennsylvania and New York are expected to lose seats as Florida, Texas, Arizona and Nevada are likely to gain seats.