A Combined Statistical Area (CSA) is a grouping of adjacent metropolitan and/or micropolitan statistical areas (MSAs) in the United States and Puerto Rico. The United States Office of Management and Budget (OMB) defines combined statistical areas based on social and economic ties measured by commuting patterns between adjacent MSAs. The areas that combine retain their own designations as metropolitan or micropolitan statistical areas within the larger combined statistical area. The primary distinguishing factor between a CSA and an MSA is that the social and economic ties between the individual MSAs within a CSA are at lower levels than between the counties within an MSA. CSAs represent multiple metropolitan or micropolitan areas that have a moderate degree of employment interchange. CSAs often represent regions with overlapping labor and media markets.