Each year the U.S. Census Bureau releases migration flow tables for selected geographic summary levels based on the American Community Survey (ACS) 5-year dataset. County-to-county and county/minor civil division (MCD)-to-county/MCD migration flow estimates have been produced for every 5-year ACS dataset beginning with the ACS 5-year 2005-2009 estimates. Flows between metropolitan statistical areas (MSAs) were introduced with the 2009-2013 dataset and have been produced for each subsequent dataset. The 2008-2012 table package was the first in the series to include migration flows from municipios in Puerto Rico to counties (and equivalents) in the fifty states plus District of Columbia. In addition, the county-to-county flows going back to 2006-2010 dataset are available through the Census Flows Mapper. As of 2016, all ACS migration flows data for counties, MCDs, and MSAs were made available in the Census application programming interface (API) through the Census Developers site.