Bivariate Choropleth Map- Poverty statistics of America

This bivariate map is very interesting as it portrays the 50 states of the U.S. and the distribution of poverty in the states.  There seems to be a dividing line in the middle of the country, with the Northern half of the country experiencing very low poverty rates, while the Southern half of the country experiencing very high poverty rates.  One might often think the opposite of what the data portrays, with the favorable climate of the south, yet the numbers don't lie.
http://www.cdc.gov/pcd/issues/2007/oct/07_0091.htm