sentences:  List of micropolitan statistical areas
  
  The United States Office of Management and Budget (OMB) has defined 550 micropolitan statistical areas (μSAs) for the United States and five for Puerto Rico.The OMB defines a Micropolitan Statistical Area as one or more adjacent counties or county equivalents that have at least one urban core area of at least 10,000 population but less than 50,000, plus adjacent territory that has a high degree of social and economic integration with the core as measured by commuting ties.