D.C. Code § 47-706: System to be used outside City — Plat books.

The Mayor of the District of Columbia shall cause to be prepared a series of volumes of plats, on a scale of 100 feet to the inch, embracing all the land in said District outside the City of Washington, these plats to show at all times the separate parcels of land created by subdivisions, sales, wills, condemnations, dedications, decrees of court, or otherwise, each with its distinctive number. Said books shall be kept in the Office of the Surveyor of said District, and shall be numbered according to the first and last page numbers of each volume, the pages being numbered continuously, and indefinitely rising in numbers as new books are opened to record changes in the outlines of parcels from any cause.