Every square foot of land within a municipality is impressed with legal qualities, which are often more lasting than pavements or buildings or other physical structures. Once a strip of land becomes dedicated to the public as a street or park it is likely to remain a street or park for centuries. Sites for schools and other public buildings, owned by the city, commonly long remain its property. Privately-owned land may receive a legal impress of more or less enduring character through limitations imposed by a zoning ordinance. The location of street railways, sewers, water-supply systems, gas and electric conduits, and overhead wires is based on legal sanctions.

The legal status given to land within a city forms the basis of a plan, whose value to the community depends mainly on the forethought that was used in the past in assigning legal qualities to land. Good and bad decisions become so embodied by force of law and by physical works that follow, that in many cases it is impracticable to alter them. Wise decisions now and in years to come depend mainly on proper planning, so that each step taken will be in accord with a consistent general scheme.