Density, Residential Buildings, and Infilling

The same number of people can occupy wildly different amounts of land depending on what kind of housing they live in. A suburb of detached single-family houses, each with its own yard, spreads a population across a lot of ground. A neighborhood of row houses sharing walls fits more units into the same space. A block of high-rise towers stacks hundreds of units vertically on a tiny footprint. Same population, ten times the land difference, just from the shape of the buildings.

This is why geographers measure residential density as housing units divided by land area, usually in units per hectare or per acre. Detached housing produces low density because each unit claims its own horizontal space. Row houses raise density by eliminating side yards and sharing walls. Towers push density highest by building upward instead of outward, letting one small parcel hold many stacked units.

Infilling connects this idea to how cities change over time. When a low-density neighborhood has vacant lots, parking lots, or underused land scattered through it, developers can add new housing directly into those gaps instead of building outward at the city's edge. Infilling raises the neighborhood's density without expanding its boundary, and it often shows up alongside gentrification, since new infill housing can raise land values and shift who can afford to live there. Density itself stays a neutral measurement of land use, separate from anything about the people living in the housing.