United States micropolitan statistical areas (µSA, where the initial Greek letter mu represents "micro-"), as defined by the Office of Management and Budget (OMB), are urban areas in the United States centered on an urban cluster (urban area) with a population at least 10,000 but less than 50,000. The micropolitan area designation was created in 2003. Like the better-known Metropolitan Statistical Areas, a micropolitan area is a geographic entity used for statistical purposes based on counties and county equivalents. The OMB has identified 576 micropolitan areas in the United States.