Associated Home Builders, Inc. v. City of Walnut Creek (Cal. 1971). In California, the Subdivision Map Act is the enabling statute for local supervision of subdivision development. Under the statute, the control of design and improvement of subdivisions is vested in the city or county with a limited right of judicial review to examine the reasonableness of the enacted ordinances. The act requires a subdivider to file a tentative map showing the design of the proposed subdivision for approval before the land can be legally sold