What is now the District of Columbia looked very different in 1792. Still part of Maryland, the area where our nation's capitol grew was largely empty land, forest and a few farms. This great map, created sometime in the 1860s, shows the pre-District plantations in 1792 and their owners' names, plus a few other interesting features -- the then-40-year old town of Georgetown and the planned towns of Hamburgh and Carrollsburgh, which never really took off. There's also Jenkins Hill, a natural promontory whose name was changed when it was used as the site of an important building: the U.S. Capitol.
Explore the map to see where you are in the old plantations -- maybe your house or office are in what was Duddington's Pasture, Widow's Mite, Jamaica or Mexico. You may also notice that Mount Pleasant is farther south than what we know by that name -- the site of the neighborhood was part of a much larger parcel with the same name that was subdivided over time. You can also see the amount of land that was filled in over time, especially downtown, on the Mall, and along the rivers.
This map only includes the area that became the City of Washington, the part of the District of Columbia that was covered by Pierre Charles l'Enfant's eponymous plan. The L'Enfant Plan was bordered by the Potomac and Anacostia Rivers, Rock Creek, and Boundary Street, which was later renamed Florida Avenue. The curving street fits the city's topography -- past Florida Ave. the flat coastal plain ends and the Piedmont plateau begins, with the land quickly gaining altitude. This flat terrain was much better suited for walking, horses and carriages.
Beyond the plan you were in Washington County or the separate District of Columbia municipalities of Georgetown, the City of Alexandria, and Alexandria County, which is now Arlington County. The Virginia portions were retroceded in 1846 and the remaining three municipalities were merged into one government in 1871. Interestingly, voters in Alexandria County actually opposed that retrocession.
Click here for a version of the map you can turn on and off or download it in KMZ format and explore for yourself in Google Earth. The fit to the real world isn't exact, but it's pretty darn good for a hand drawn map from the 1860s.
The map image is available on Library of Congress website and from Flickr user leeanncafferata.