A plat consists of a map, drawn to scale, showing the divisions of a piece of land. U.S. General Land Office surveyors drew township plats to show the distance and bearing between survey corners, and sometimes included topographic or vegetation information. City, town or village plats show subdivisions into blocks with streets and alleys.

Further refinement often splits blocks into individual lots, usually for the purpose of selling the described lots; this has become known as subdivision. After the filing of a plat, legal descriptions can refer to block and lot-numbers rather than portions of sections.

In order for plats to become legally valid, a local governing body, such as a public works department, urban planning commission, or zoning board must normally review and approve them.