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The map books are arranged alphabetically by county. The library houses a collection of bound Illinois PLAT maps, starting in the 1960s, in shelves along the central wall on the Fourth Floor. In most counties, these offices are in the county courthouse. You can obtain tax maps from the county assessors office, or subdivision plats from the office of the recorder of deeds. 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. Because the process of incorporation sometimes occurred at a courthouse, the incorporation papers for many American cities may be stored hundreds of miles away in another state. The creation of a plat map marks an important step in the process of incorporating a town or city according to United States law. After the filing of a plat, legal descriptions can refer to block and lot-numbers rather than portions of sections.
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Further refinement often splits blocks into individual lots, usually for the purpose of selling the described lots this has become known as subdivision. City, town or village plats show subdivisions into blocks with streets and alleys. General Land Office surveyors drafted township plats of Public Lands Surveys to show the distance and bearing between section corners, sometimes including topographic or vegetation information. Other English-speaking countries generally call such a document a cadastral map or plan. is a map, drawn to scale, showing the divisions of a piece of land.
