10.2 City layout

Over the past century, the proportion of all humans who live in cities has dramatically increased, reaching 56% in 2021 and expected to reach 68% by 2050.^[1] As urban populations grow, cities need to physically expand: outward, upward, or both (Fig 1). Without planning and intentional strategies for how to use land, urban development spreads uncontrollably into surrounding natural areas, creating urban sprawl. The UN reports that “between 2000 and 2020, cities sprawled up to 3.7 times faster than they densified, resulting in negative impacts on the natural environment.”^[2] Because sprawl increases the distances people have to travel across a city, it leads to dependence on personal vehicles and an increase in transportation-related GHG emissions. However, compared to rural areas, cities allow for more efficient use of resources, because having housing, schools, and businesses together in one location allows for economies of scale in infrastructure and shorter travel distances. If cities are designed to maximize this efficiency, they can be really sustainable places.

Zoning laws determine what each parcel of land in a city can be used for, such as single-family housing, apartments, mixed-use buildings (businesses on the ground floor and apartments above), parks, or factories. The placement and density of these different options shapes the urban environment. Zoning decisions can reflect bias and perpetuate injustice. For example, in the United States in the 1930s, each neighborhood in many large cities was rated at one of four levels of desirability for homeowners’ loans, and areas with non-White and/or immigrant populations were often assigned the lowest rating. This practice, called redlining, made it harder for people in those communities to buy homes and advance economically, and it also influenced infrastructure and land use in those areas, such as parks that provide recreational opportunities or industrial facilities that produce pollution. Redlined areas were associated with increased health risks, less greenspace, increased crime, and persistent poverty.^[3] These effects persist to the present day, decades after the practice was ended. In the southeastern United States, minority communities have significantly higher levels of soil contamination than white communities.^[4]

City planners can promote approaches to development that decrease the environmental impacts of city layout. The first policy tool is mixed-use zoning, which allows housing and businesses to be interspersed in the same area (Fig 2). People might live in apartments above a bank or grocery store and be within walking distance of a school, a park, and a doctor’s office. This decreases pollution from transportation and increases people’s access to essential services and resources. Another city planning solution is to fill in low-density areas by replacing things like parking lots and single-story businesses with apartments or a mixed-use zone. Finally, when cities do expand outward, they can do so in a way that allows for efficient, low-emission living and movement around the city. One example of this is Copenhagen, Denmark’s 1947 Finger Plan, which set up new development in five lines radiating from the city center, each served by public transportation and separated by preserved natural areas so that people living along each line had easy access both to the city center and to greenspace near their homes. Another example comes from Freiburg, Germany, whose government set environmental, transportation, and energy guidelines for new developments, involving dense, mixed-use neighborhoods, tram lines connecting to the city center and train station, limited parking (in communal, solar-powered garages), preserved greenspace, and rainwater retention systems.^[5]

Knowledge Check

Take a moment to complete the short quiz below to assess your understanding of this section. Read each question carefully and refer to the section content as needed. This quiz is not graded – it’s simply an opportunity for you to reflect on what you’ve learned and reinforce key concepts.