How can the same country look almost empty — and unbelievably crowded?
Same counties. Same population. Three different density thresholds.
Nearly Empty
Dense
Extremely Dense
Nearly half of U.S. land holds just 1.3% of Americans, while 1.8% of the land holds almost 40%. Nothing about the country changes between these maps; only the density cutoff does.
A threshold is a choice, and it decides the story a map tells. Before trusting a map of “empty” or “crowded” places, ask where the cutoff was set.
Who chose the cutoff in the last chart that surprised you?
How should I read these three maps?
These three percentages are not supposed to add up to 100%. The maps show three selected slices of the density distribution rather than dividing every county into three complete categories.
Dense shows counties from 500–999.
Extremely Dense shows counties at 1,000 or more.
Counties from 10–499 people per square mile are intentionally left out so the contrast between the sparse and crowded ends of the distribution is easier to see.
Each county or county-equivalent unit can appear in only one of the three displayed ranges—but many appear in none of them.
The underlying population does not change from map to map. Only the threshold changes. That is why choosing a cutoff can dramatically change the picture a map seems to show.
Why 10 people per square mile for “nearly empty”?
The threshold is close to the population-density benchmark historically associated with the U.S. frontier. It is not a claim that these counties are literally empty; it is a way to make the uneven distribution of population visible.
The same gap between land and people shows up at the scale of the whole planet: one circle drawn around southern China holds more than half of humanity, while still covering plenty of nearly empty land. A map colored by territory instead of population is quietly measuring the wrong thing.
On the Extremely Dense map, which cities are highlighted, and which surprising ones aren’t?
Phoenix, Las Vegas, and San Diego — major cities that aren’t highlighted
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 dark 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 dark area just north of Denver.
Virginia — what are all those tiny dark 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 is still highlighted
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 dark shapes.
Some sprawling Sun Belt metros are highlighted
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. These maps use 2023 boundaries so the map and its 2023 density data describe the same geographic units.
The highlighted 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.