The United States federal government defines and delineates the nation's metropolitan areas for statistical purposes, using a set of standard statistical area definitions. As of 2013, the U.S. Office of Management and Budget (OMB) defined and delineated 388 metropolitan statistical areas (MSAs) and 541 micropolitan statistical areas (µSAs) in the United States and Puerto Rico. Many of these 929 MSAs and µSAs are, in turn, components of larger combined statistical areas (CSAs) consisting of adjacent MSAs and µSAs that are linked by commuting ties; as of 2013, 524 metropolitan and micropolitan areas are components of the 169 defined CSAs.