As defined by the Bureau of the Census, an area that includes 1 or more incorporated cities, villages and towns (central place) and the adjacent densely settled surrounding territory (urban fringe or suburbs) that together have a minimum of 50,000 persons. The urban fringe generally consists of at least 1000 persons per square mile and areas such as industrial parks and railroad yards, if they are within areas of dense urban development. (APTA) (TRB)