AP Human Geography 6.6: Density and Land Use

A city's residential land use is the land it gives to housing and the pattern that housing makes. One way to describe the pattern is housing density: how many housing units, the homes one household can live in, stand on each acre of land. Housing falls into three levels.

Low-density housing is detached single-family houses, each on its own lot with a yard and usually a driveway. Few homes fit on an acre, so homes spread over a lot of land, stores and jobs sit far away, and most trips are made by car.

Medium-density housing fits several homes on the land one house would use: townhouses and row houses that share side walls, duplexes, and apartment buildings of two to four floors. Yards are small or shared, and enough people live within a walk to support a corner store or a bus line.

High-density housing is apartment and condominium buildings many floors tall, reached by elevators. Hundreds of homes can stand on a few acres, with shared parks instead of private yards, and enough people within a short walk to support rail transit and street-level shops.

The blocks are hypothetical, like every place and number in this lesson. Real cities draw the lines between the levels in different places, so describe a neighborhood by its buildings and its homes per acre rather than by one cutoff.

Residential buildings and land use reflect a city's culture and technology: they show what people valued, what they could build and how they could travel when the homes went up. They also shape the city: once built, they steer how people live for decades.

Technological capabilities. Before mechanized transportation most people walked to work, so homes were packed close to workplaces, and without elevators buildings stopped at a few floors. Streetcar and commuter rail lines let homes spread outward along their routes. Cars and highways let homes spread across large lots far from any job, the low-density pattern often called sprawl. Steel frames and electric elevators made high-density towers possible.

Culture. What households value and expect shows in housing too. Where owning a detached house with a private yard is a common goal, cities build wide areas of low-density housing, and zoning laws that allow only detached houses on most blocks write that value into the land. Where apartment living is ordinary, or several generations of a family live together, cities build other forms: more apartments, or larger homes around shared courtyards.

Shaping. A low-density suburb, once built, makes a car close to necessary and is hard to serve with buses or trains. A dense neighborhood makes walking, transit and corner shops workable.

Cities do not grow at a steady pace. They grow in cycles of development: a wave of building when the economy booms or new transportation opens land, then a slowdown, then a later wave. Each wave builds in the way its own era's technology and culture allowed, and the buildings outlast the era. So a city's housing is layered by age, a little like the rings of a tree trunk. Where a city grew outward ring by ring, the oldest, densest housing sits near the center, and later rings are often built at lower density than earlier ones.

Neighborhoods have cycles of their own. A new neighborhood is built, fills and ages. As buildings wear out and households with more money move to newer areas, old homes may be divided into smaller units, left empty or torn down. Later, when land near the center is in demand again, the neighborhood may be rebuilt, often at a higher density than before.

That makes the age of housing a piece of evidence. When you compare neighborhoods, ask when each one's housing was built and what builders and residents could do then, and look for places a later wave rebuilt.

Infilling is building new homes or other uses on vacant or underused land inside an area that is already built up: an empty lot, a surface parking lot, an old rail yard or factory site, or the back of a large house lot. It is the opposite of building on open land at the city's edge. What makes a project infill is where it is built, not its size: one small house on an empty lot and a tall tower on a parking lot both count.

Infilling raises density without adding land. A parking lot near downtown becomes a six-story apartment building; a large lot gets a second, smaller house behind the first. The new homes use roads, water pipes, sewers and transit lines that are already there, and they put more people within walking distance of shops and jobs.

Infilling reflects and shapes the city like any other building. It comes in a later cycle of development, when land in the built-up area is in demand, when building technology makes tall buildings on small sites affordable, or when more residents want to live close in. Once built, it changes daily life on the block: more neighbors, more customers for local shops, more traffic, and sometimes higher rents.