How much of America holds 40% of its people?
Just 1.8% of the land.
Which places are highlighted—and which surprising cities aren’t?
Phoenix, Las Vegas, and San Diego — major cities that aren’t blue
All three sit inside very large counties. Phoenix is in Maricopa County, Las Vegas in Clark County, and San Diego in San Diego County. Their dense urban populations are averaged together with much larger, less-populated areas, pulling countywide density below this map’s 1,000-person threshold. The city can be dense even when its county isn’t.
Denver and Broomfield — why are those small blue spots there?
Both have unusually compact city-county boundaries. Denver is a consolidated city and county, while Broomfield is also organized as the City and County of Broomfield. With much less surrounding rural land included, their countywide densities remain above the threshold. Broomfield is the smaller blue area just north of Denver.
Virginia — what are all those tiny blue shapes?
Virginia has many independent cities that the Census treats as county equivalents. That is why places such as Alexandria (~10,394/sq mi), Falls Church (~7,177), Charlottesville (~4,391), Richmond (~3,826), Roanoke (~2,285), and Lynchburg (~1,624) appear as tiny separate units.
New York City — one city becomes five county units
The five boroughs correspond to five county-level units: New York, Kings, Bronx, Queens, and Richmond. Manhattan’s New York County exceeds 70,000 people per square mile, while all five clear the threshold easily.
Los Angeles — a large county that still turns blue
Los Angeles County covers a large area, but its population is concentrated enough to average about 2,380 people per square mile. That makes it a useful contrast with Phoenix and Maricopa County.
Baltimore and St. Louis — cities that function like counties
Both Baltimore city (~6,983/sq mi) and St. Louis city (~4,565/sq mi) are independent county-equivalent units, so they show up as compact blue shapes.
Some sprawling Sun Belt metros do turn blue
Dallas County (~2,985/sq mi), Harris County around Houston (~2,833), Fulton County around Atlanta (~2,049), Miami-Dade (~1,414), and Davidson County around Nashville (~1,415) all exceed the threshold.
Connecticut looks different in current Census geography
Beginning with newer Census geography, Connecticut’s nine planning regions are treated as county equivalents. H013 uses 2023 boundaries so the map and its 2023 density data describe the same geographic units.
The blue areas do not simply show where cities are. They show where dense populations happen to line up with county or county-equivalent boundaries. Change the unit—from counties to cities, census tracts, or urban areas—and the map changes too.
What changes when we measure where people are instead of where land is?
Sources: U.S. Census Bureau, Vintage 2023 Population Estimates and 2023 Gazetteer Files. County and county-equivalent boundaries: U.S. Census Bureau, 2023 cartographic boundary files. Puerto Rico excluded. The 1,000-people-per-square-mile threshold identifies 159 county or county-equivalent units. Connecticut is shown using its nine Census county-equivalent planning regions.