A plat is a map that shows how land is divided, typically in a subdivision. Subdivision platting occurs when a large parcel of land is separated into multiple, smaller parts of land.
Platting is typically done to create segments of land that will be developed into a neighborhood. Subdivision platting is typically done by a land surveyor. Plat maps show the boundaries of property lines. Roads and other public resources are also shown on plat maps. Plat maps also typically include the building number and approximate lot dimensions. Plat maps also include a tract number and often the name of the subdivision, if one has been decided.
A plat is technically a legal description of a specific property and is required when land is going to be divided. Not all land is platted -- land described by metes and bounds has not been platted. A plat that has been changed is called a "replat." A plat tells consumers about the size and shape of the land, which makes it especially useful when buying or selling a property. In most areas, a local governing body has to review and approve the proposed plat map. This is to ensure that all rules and regulations are being enforced.