How city area is measured in the United States

What "city" means in the United States

In Census Bureau statistics, a city is an incorporated place: a place legally in existence under its state's law, set up to provide government for a concentration of people. A place lies within a single state but can cross county lines. Counties are a separate level of government, and in some states towns are treated as minor civil divisions rather than places. Census Designated Places are the unincorporated, purely statistical counterpart.

Consolidated city-counties are the main reason one US city can be very large. The Census Bureau's glossary defines a consolidated government as one in which the functions of an incorporated place and its county have merged. In Jacksonville, Florida, the city and county governments merged on 1 October 1968, according to Wikipedia's Jacksonville article, and the Census publishes a single "Jacksonville city" row covering the consolidated city. San Francisco is also a combined city and county; the city's own resilience plan refers to "the City and County" when it gives its area. The difference is scale: San Francisco's land area is a small fraction of Jacksonville's.

Two larger Census geographies are often mistaken for the city. Urban Areas are densely developed territory, built from 2020 Census blocks; to qualify, an area needs at least 2,000 housing units or a population of at least 5,000. Because they are built from blocks rather than city limits, one Urban Area can span several cities, as the name of the San Francisco--Oakland Urban Area shows. Metropolitan Statistical Areas are built from whole counties: the counties around an Urban Area of at least 50,000 people, plus adjacent counties linked to it by commuting. We do not publish Urban Area figures here, because we could not find an independent second source for them.

Every Census Gazetteer area figure comes as a pair. Land area and water area are listed separately, and the water figure includes inland, coastal, Great Lakes and territorial sea water. The Gazetteer gives no total; adding the two is your own calculation, not an official figure.

Why our map may show a different number

When we have no stored boundary for a city, the app sends OpenStreetMap's Nominatim service a search for the city name and country, restricted to cities. On 17 October 2026, "Jacksonville, United States" returned the Jacksonville administrative boundary (OpenStreetMap relation 119008, administrative level 8), displayed as "Jacksonville, Duval County, Florida, United States". "San Francisco, United States" returned relation 111968, which OpenStreetMap tags at administrative level 6, the county level, because the city and county share one boundary. "New York, United States" returned the New York City boundary, relation 175905, at administrative level 5. All three results are relations with their own polygons; the app draws a result like that directly and does not mark it approximate.

When we have no stored area for a boundary, the map calculates the area from the polygon, not from the Census. The OpenStreetMap polygon follows the city limits, and in all three cities those limits run out across water, so an area measured from it counts land and water together. For Jacksonville, San Francisco and New York City, the polygon area is within one percent of the Census land and water figures added together, and well above the land figure alone. San Francisco shows the effect most: its polygon reaches the Farallon Islands, which the city's resilience plan places about 30 miles off the Pacific coast, and the Census lists 479.7 km²^5,6 of water against 120.9 km²^3,4 of land.

If you compare an area measured from one of these polygons with a Census figure, compare it with land and water together, not with land area. Even then, the two differ slightly.

Problems getting boundaries in the United States

The first problem is water. For a coastal city the water figure can be large: San Francisco's is several times its land area. The Census Bureau also warns that its identification of land and water is "for data presentation purposes only and does not necessarily reflect their legal definitions", so the split between them is a statistical convention, not a legal line.

The second problem is vintage. The Census Gazetteer is reissued every year, and the figures differ slightly between editions. The figures on this page come from the 2026 Gazetteer. Wikipedia's city-by-area list, which we cite as a second source, rounds to one decimal place, so its numbers differ slightly from the 2026 values; each difference is well under one percent. City infoboxes on Wikipedia may use older editions. Always check which edition a figure comes from.

The third problem is publishers. A city may publish its own figure that differs from the Census. New York City's Department of City Planning publishes a land area for the city that is not the same as the Census land area; we could not find an independent second source for the planning department's figure, so it is not shown here. San Francisco's resilience plan gives its land and water areas in whole square miles, close to the Census values.