The metropolitan region may roughly be defined as the area within commuting distance of the central or mother city. It may be an area about one or two cities of small or medium size as well as that about a large city. It may at present.contain only one or two units of really urban character, the rest of the region being residential suburban. But if it does not have other urban units now, it will acquire them later as population increases and neighborhood business districts develop. Moreover in this day, when every chamber of commerce is seeking factories and when factory managements are thinking in terms of industrial distribution, it is almost inevitable that the metropolitan region outside the mother city will develop industrial districts. Consequently, provision must be made in the regional plan for both industrial areas and commercial areas in addition to residential areas. These, normally, will grow into separate towns. And, unless preventive measures are taken, they ultimately will merge into one great city, as Philadelphia and its satellites have done.

Philadelphia has developed much as the regional planner would have a city develop, except that adequate provision was not made for traffic and except that the separate communities were not kept separate by adequate intervening open spaces. The original city of Philadelphia with its mill satellites, Kensington and Manayunk; its factory satellites, Nice-town and Tacony; its residential satellites, Germantown and Chestnut Hill, if each were separated from the others by open areas, if the brook valleys had been preserved instead of being filled up to make uncertain sites for the foundations of buildings, would be a pleasanter city than it is with its interminable streets filled with monotonous rows of houses.....