The District has a total area of 68.3 square miles (177 km2), of which 61.4 square miles (159 km2) is land and 6.9 square miles (18 km2) (10.16%) is water. It is no longer 100 square miles (260 km2) due to the retrocession of the southern portion of the District back to the Commonwealth of Virginia in 1846. The city is therefore surrounded by the states of Maryland to the southeast, northeast, and northwest and Virginia to the southwest.
Washington has three major natural flowing streams: the Potomac River and its tributaries the Anacostia River and Rock Creek. Tiber Creek, a natural watercourse that once passed through the National Mall, was fully enclosed underground during the 1870s. The creek also formed a portion of the now-filled Washington City Canal, which allowed passage through the city to the Anacostia River from 1815 until the 1850s. The present Chesapeake and Ohio Canal starts in Georgetown and was used during the 19th century to bypass the Great Falls of the Potomac River, located upstream (northwest) of Washington.
The highest natural elevation in the District of Columbia is 409 feet (125 m) above sea level at Fort Reno Park in northwest Washington. The lowest point is sea level at the Potomac River. The geographic center of Washington is located near the intersection of 4th and L Streets NW.[ Contrary to the urban legend, Washington was not built on a reclaimed swamp but wetlands did cover areas along the water. The United States government owns about 23% of the land in the District; lower than the percentage of federal lands in 12 states.
The District has 7,464 acres of parkland, about 19% of the city's total area and the second-highest percentage among high-density U.S. cities. The large percentage of city land dedicated to park areas contributes to a high urban tree canopy coverage of 35%. The National Park Service manages most of the city's parkland, including Rock Creek Park, the Chesapeake and Ohio Canal National Historical Park, the National Mall and Constitution Gardens, Theodore Roosevelt Island, Fort Dupont Park, Meridian Hill Park, Kenilworth Park and Aquatic Gardens, and Anacostia Park. The only significant area of natural habitat not managed by the National Park Service is the U.S. National Arboretum, which is operated by the U.S. Department of Agriculture.
Washington is located in the humid subtropical climate zone (Köppen: Cfa) and exhibits four distinct seasons. Its climate is typical of Mid-Atlantic U.S. areas removed from bodies of water. The District is located in plant hardiness zone 8a near downtown, and zone 7b elsewhere in the city, indicating a temperate climate.
Spring and fall are warm, while winter is cool with annual snowfall averaging 14.7 inches (37 cm). Winter temperatures average around 38 °F (3.3 °C) from mid-December to mid-February. Summers are hot and humid with a July daily average of 79.2 °F (26.2 °C) and average daily relative humidity around 66%, which can cause medium to moderate personal discomfort. The combination of heat and humidity in the summer brings very frequent thunderstorms, some of which occasionally produce tornadoes in the area.
Blizzards affect Washington on average once every four to six years. The most violent storms are called "nor'easters", which often affect large sections of the U.S. East Coast. Hurricanes (or their remnants) occasionally track through the area in late summer and early fall, but are often weak by the time they reach Washington, partly due to the city's inland location. Flooding of the Potomac River, however, caused by a combination of high tide, storm surge, and runoff, has been known to cause extensive property damage in Georgetown.
The highest recorded temperature was 106 °F (41 °C) on July 20, 1930, and August 6, 1918, while the lowest recorded temperature was −15 °F (−26 °C) on February 11, 1899, during the Great Blizzard of 1899. During a typical year, the city averages about 37 days at or above 90 °F (32.2 °C) and 64 nights at or below freezing.
Washington, D.C., is a planned city. In 1791, President Washington commissioned Pierre (Peter) Charles L’Enfant to design the new capital. A French-born architect and city planner, L'Enfant first arrived in the colonies as a military engineer during the American Revolutionary War. The L'Enfant Plan for Washington featured broad streets and avenues radiating out from rectangles, providing room for open space and landscaping. He based his design on plans of cities such as Paris, Amsterdam, Karlsruhe, and Milan brought from Europe by Thomas Jefferson in 1788. L'Enfant's design also envisioned a garden-lined "grand avenue" approximately 1 mile (1.6 km) in length and 400 feet (120 m) wide in the area that is now the National Mall.
In March 1792, President Washington dismissed L'Enfant due to his insistence on micromanaging the city's planning, which had resulted in conflicts with the three commissioners appointed to supervise the capital's construction. Andrew Ellicott, who had worked with L'Enfant surveying the city, was then tasked with completing the design. Though Ellicott made revisions to the original plans, including changes to some street patterns, L'Enfant is still credited with the overall design of the city.
By the start of the 20th century, L'Enfant's vision of a capital with open parks and grand national monuments had become marred by slums and randomly placed buildings, including a railroad station on the National Mall. In 1900, Congress formed a joint committee, headed by Senator James McMillan, charged with beautifying Washington's ceremonial core. What became known as the McMillan Plan was finalized in 1901. It included the re-landscaping of the Capitol grounds and the Mall, constructing new federal buildings and monuments, clearing slums, and establishing a new citywide park system. Architects recruited by the committee kept much of the city's original layout, and their work is thought to have largely preserved L'Enfant's intended design.
By law, Washington's skyline is low and sprawling. The first building height restrictions in D.C. were put in place following the construction of the twelve-story Cairo Apartment Building in 1894. The Heights of Buildings Act of 1910 amended the restrictions to allow buildings that are no taller than the width of the adjacent street, plus 20 feet (6.1 m). Despite popular belief, no law has ever limited buildings to the height of the United States Capitol or the 555-foot (169 m) Washington Monument, which remains the District's tallest structure. City leaders have criticized the height restriction as a primary reason why the District has limited affordable housing and traffic problems caused by urban sprawl.
The District is divided into four quadrants of unequal area: Northwest (NW), Northeast (NE), Southeast (SE), and Southwest (SW). The axes bounding the quadrants radiate from the U.S. Capitol building. All road names include the quadrant abbreviation to indicate their location, and house numbers are assigned based on the approximate number of blocks away from the Capitol. In most of the city, the streets are set out in a grid pattern with east–west streets named with letters (e.g., C Street SW) and north–south streets with numbers (e.g., 4th Street NW).
The City of Washington was bordered by Boundary Street to the north (renamed Florida Avenue in 1890), Rock Creek to the west, and the Anacostia River to the east. The city's streets were extended throughout the District starting in 1893, and Georgetown's streets were renamed in 1895. Some streets are particularly noteworthy, such as Pennsylvania Avenue, which connects the White House to the U.S. Capitol and K Street, which houses the offices of many lobbying groups. Washington hosts 176 foreign embassies, many of which are located on a section of Massachusetts Avenue informally known as Embassy Row.