U.S Appropriations are lands set aside at the time of the original founding and platting of the city for use by the U.S. Federal Government.  The White House, for instance, Treasury Building, Ellipse and LaFayette Park all sit on Appropriation No. 1.  D.C General Hospital is on Appropriation No.13 (with the consent of the Federal Government). Appropriations are often confused with U.S Reservations but the two terms are not interchangeable.  There are 17 U.S Appropriations in Washington, D.C., all of which are located within the limits of the Original City and, by definition; there can never be any more.
Appropriation layers in VPM are (point, line, poly) - AppropriationPT, AppropriationLN, AppropriationPLY