The 1791 L'Enfant Plan of the City of Washington, DC, shows a tidy and intricate grid of streets and diagonal avenues, with squares, rectangles, and circles at many of the major intersections. The green space of the future National Mall and President's Park is also visible. The plan, which is centered between the Potomac River and Eastern Branch (Anacostia River), narrows as the two waterways meet at Greenleaf's Point, the future home of the Washington Arsenal and, later, Fort McNair. The plan is so significant to Washington and the nation's history that it was officially designated and added to the National Register of Historic Places in 1997.

Despite its detail, the plan ends abruptly, with a lot of blank space on the map. Nothing is shown west of the Potomac, part of the District until 1847, or east of the Anacostia. Georgetown, a separate city with its own government, is shown with limited detail, and north of Georgetown and the proposed City of Washington is more blank space.

The vast area outside of the City of Washington and Georgetown became Washington County, a rural landscape of farms, estates, and plantations. Throughout much of the 19th century there was a boundary between the City of Washington and the areas to the west, north, and east. In fact, there was even a Boundary Street (today's Florida Avenue). The three jurisdictions would finally consolidate following the Organic Act of 1871. This tour traces that northern boundary and the many historic landmarks and districts that can be found along its path. Many important buildings and structures have been constructed along this boundary, in a variety of architectural styles, and the adjacent landmarks and districts have witnessed important social history, which is both locally and nationally significant.

The original boundary starts on the west end, where Rock Creek meets the Potomac. Here, west of Rock Creek, is Georgetown. Therefore, this was a natural boundary marker for L'Enfant as he sketched out his plan. Just north of the river is the start of the Chesapeake & Ohio Canal, a critical transportation link to Cumberland, Maryland and points farther west.

As Rock Creek winds slightly to the east, the boundary does as well. At roughly 22nd Street, 23rd Street, and Massachusetts Avenue NW, the boundary breaks from Rock Creek and moves to the northeast. Here, L'Enfant followed another natural boundary marker, the escarpment. Washingtonians have likely noticed this escarpment, or slope, as the elevation increases north of Florida Avenue, particularly between Connecticut and Sherman avenues. North of here the District's topography becomes more varied and challenging, especially for 18th century transportation. Therefore, this was a natural end point for the L'Enfant Plan.

Florida Avenue (Boundary Street) continues northeast past Meridian Hill Park and Cardozo Senior High School before abruptly turning south between 11th and 9th streets NW. The boundary then goes in a southeast direction until 15th Street NE. This southeast diagonal is apparent to anyone traveling up or down Florida Avenue between U Street and Benning Road. This stretch also includes many historic neighborhoods, including LeDroit Park and Bloomingdale, as well as Union Market and Gallaudet University. LeDroit Park is particularly significant, as this "suburb" was built just north of the city, starting in the 1870s. It was new residential subdivisions like this — which did not conform to the L'Enfant Plan — that prompted Congress to pass the Subdivision Act of 1888 and then the Permanent Highway Act of 1893. Because of these laws, many of the neighborhoods developed in the former Washington County have an orderly grid, intersected with grand avenues and circles (e.g., Petworth's Grant and Sherman circles) — although, many streets ended up being platted with some respect to the topography. Following pushback, subdivisions platted prior to the law's passage were incorporated into the new street layout and their somewhat haphazard street layout can still be seen today (e.g., Columbia Heights and Mount Pleasant).

Also in the 1890s, Boundary Street officially became Florida Avenue — further illustrating the desire to continue the L'Enfant Plan northward. This also explains Florida Avenue's unique path as it twists and turns around the city.

The boundary then moves south along 15th Street NE, before turning eastward along C Street NE. When looking at the L'Enfant Plan, the northern boundary ends without fanfare — no major avenue, circle or square — at the Anacostia River, another natural boundary marker. Today, this area is known as Kingman Park and is just north of the former RFK Stadium.

Today, the boundary is not officially marked, but there are many reminders of it as Washingtonians move through the city, whether exercising along the District's waterways or commuting along Florida Avenue. This tour seeks to highlight this significant history and the important historic sites found along this pathway.