A zoning ordinance is a rule made by an Authority Having Jurisdiction (AHJ) that delineates what areas are acceptable for residential or commercial use.
Zoning ordinances change depending on your cities and states. To find specific zoning laws you should research whatever area you are planning to build in. For construction professionals zoning ordinances are followed to determine what a building is being used for. Before construction begins zoning ordinances will have been reviewed and the building specifications and plans will reflect what the building's final use case will be.
In Austin, Texas areas that are zoned for apartments and condos must meet a cap ratio (#aprtments/lot size). The most common zoning requirement in all cities is a limit on building heights, but these may be nonexistent or vary greatly depending on the city.
