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A simulated-color image of Houston taken on NASA's Landsat 7 satellite with Galveston Bay and Galveston Island visible in the picture

According to the United States Census Bureau, the city has a total area of 601.7 square miles (1,558.4 km²) — 579.4 square miles (1,500.7 km²) of it is land and 22.3 square miles (57.7 km²) of it is water. The total area is 3.7 percent water.

Houston is located in the gulf coastal plains biome, and its vegetation is classified as temperate grassland. Much of the city was built on forested land, marshes, swamp, or prairie—all of which can still be seen in surrounding areas.

Much of Houston is very flat, making flooding a recurring problem for its residents. The city stands about 50 feet above sea level—the highest area within city limits being 90 feet.^[1] The city once relied on groundwater for its water needs, but land subsidence forced the city to turn to ground-level water sources such as Lake Houston.

Houston has four major bayous passing through the city: Buffalo Bayou, which runs into downtown and the Houston Ship Channel; and three of its tributaries: Brays Bayou, which runs along the Texas Medical Center; White Oak Bayou, which runs through the Heights and near the northwest area; and Sims Bayou, which runs through the south of Houston and downtown Houston. The ship channel goes past Galveston and into the Gulf of Mexico.

Underpinning Houston's land surface are unconsolidated clays, clay shales, and poorly-cemented sands up to several miles deep. The region's geology developed from stream deposits from the erosion of the Rocky Mountains. These sediments consist of a series of sands and clays deposited on decaying organic matter that, over time, transformed into oil and natural gas. Beneath these tiers is a water-deposited layer of halite, a rock salt. The porous layers were compressed over time and forced upward. As it pushed upward, the salt dragged surrounding sediments into dome shapes, often trapping oil and gas that seeped from the surrounding porous sands. This thick rich soil also provides a good environment for rice farming in suburban outskirts that the city continues to grow into near Katy. Evidence of past rice farming is even still evident in developed areas as there is an abundance of rich dark loamy top soil.

The Houston region is generally earthquake-free. While the city of Houston contains 86 mapped and historically active surface faults with an aggregate length of 149 miles (240 km),^[2] the clay below the surface precludes the buildup of friction that produces ground shaking in earthquakes. These faults generally move at a smooth rate in what is termed "fault creep."

Skyline District of Downtown

When Houston was established in 1837, the city's founders—John Kirby Allen and Augustus Chapman Allen—divided it into political geographic districts called "wards." The ward designation is the progenitor of the current-day Houston City Council districts—there are nine in all.

Locations in Houston are generally classified as either being inside or outside Interstate 610, known as the "610 Loop" or "The Loop". Inside the loop generally encompasses the central business district, and has come to define an urban lifestyle and state of mind. The appellation “inner looper” carries with it the expectation of someone who appreciates cosmopolitan-style city life.

The outlying areas of Houston, the airports and the city's suburbs and enclaves are outside the loop. Another ring road, State Highway Beltway 8 (also known simply as the "Beltway"), encircles the city another 5 miles (8 km) farther out. The third ring road, State Highway 99 (also known as the Grand Parkway), is under construction.

Houston, being the largest city in the United States without zoning laws, has grown in an unusual manner. Rather than a single "downtown" as the center of the city's employment, five additional business districts have grown throughout the inner-city—they are Uptown, Texas Medical Center, Greenway Plaza, Westchase, and Greenspoint. If these business districts were combined, they would form the third-largest downtown in the United States. The city also has the third-largest skyline in the country (after New York City and Chicago), but because it is spread over a few miles, pictures of the city show—for the most part—the main downtown area.

Further information: Geographic areas of Houston

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Areas	Downtown | Uptown | Texas Medical Center | Midtown | Neartown | Museum District | Upper Kirby | Greenway Plaza | Rice Village | Westchase | Greenspoint
Communities	Acres Homes | Addicks | Aldine | Alief | Braeburn | Braeswood Place | Clear Lake City | Genoa Township | Harrisburg | Houston Heights | Independence Heights | Inwood Forest | Kingwood | Maplewood | Memorial | Meyerland | Northshore | Oak Forest | River Oaks | Sharpstown | South Park | Spring Branch | Sunnyside See also: The six wards of Houston and List of Houston neighborhoods
Enclaves	Bellaire | Bunker Hill Village | Hedwig Village | Hilshire Village | Hunters Creek Village | Piney Point Village | Southside Place | Spring Valley | West University Place