Clarence Arthur Perry (1872-1944) was an American planner who developed the concept of the neighborhood unit, which had a huge impact on urban planning worldwide. Perry believed that cities should be built (or rebuilt) to consist of an agglomeration of smaller units, typically centred on and served by an elementary school, and bounded by major roads with shopping centres at intersections. Children of such units would be able to walk to their local school without having to cross major roads; the limited size of the units (typically 6-10,000 inhabitants) would, he believed, encourage community spirit. The theory was first publicised in 1939 in Housing for the Mechanic Age and gained rapid acceptance. Perry was a founder of the Regional Planning Association of America, and had authored the RPAA's Regional Plan of New York and its Environs (1929).