No good for cities or for their design, planning, economics, or people, can come of the emotional assumption that dense city populations are, per se, undesirable. In my view, they are an asset. The task is to promote the city life of city people, housed, let us hope, in concentrations both dense enough and diverse enough to offer them a decent chance at developing city life.” —Jane Jacobs, The Death and Life of Great American Cities

It seems normal these days for people to opine on current issues without the slightest interest in understanding them. Take immigration, for example. The loudest voices against “illegal aliens” come from places that have very few recent, non-white immigrants. Those who live in diverse communities are relatively happy, thank you. Another example is the crime-ridden hellholes of Gotham and other major cities, at least in the perception of those who don’t actually live there. We who do are quite happy, thank you.

Density is another trope. To be fair, planners and urbanists have done a pretty poor job at explaining the benefits of urban density, giving NIMBYs free range to decry it as the road to perdition. And to be fair, again, density is not without its challenges, especially if it’s not planned for and left to run amok.

The pitfalls of density are numerous.

Infrastructure Strain: This is often the most immediate issue. High population density puts pressure on transportation systems, leading to traffic congestion and overcrowded public transit. Water, sewage, and electrical systems may struggle to keep pace with demand, sometimes resulting in service disruptions or quality issues.

Housing Affordability: As density increases, affordability often worsens. Competition for limited space drives up real estate prices, making it difficult for middle- and lower-income residents to afford housing. This can lead to gentrification that displaces longtime community members.

Environmental Concerns: These become more complex in dense areas. Air quality can suffer from increased vehicle emissions. Urban heat islands form as concrete and asphalt absorb sunlight, making cities significantly warmer than surrounding areas. Green space becomes scarce and highly valuable, limiting residents’ access to nature.

Quality of Life: Challenges can emerge from overcrowding. Noise pollution can increase substantially, privacy can decrease, and some people experience psychological stress from constant proximity to others. Crime rates may rise in some dense areas, though data generally show that crime per capita is less in urban areas, despite claims to the contrary.

Public Health: As we saw during the pandemic, disease can spread more rapidly in dense populations. Heavily populated cities may also struggle with waste management and sanitation challenges.

Economic Inequality: This often becomes more visible and pronounced when wealthy and poor populations live in close proximity but have vastly different access to resources and opportunities.

All this being said, many of these problems aren’t inevitable consequences of density itself. Income inequality, affordability issues, traffic woes, and crime exist everywhere. They’re brought into sharper focus in the urban environment, but that may actually make them easier to address. Some of the world’s most livable cities are also quite dense, suggesting that these issues can be managed with thoughtful urban design and policy.

Urban density offers numerous compelling advantages that help explain why cities continue to grow and thrive.

Economic Efficiency: This is perhaps the strongest benefit. Dense areas create powerful agglomeration effects when businesses, workers, and ideas cluster together, boosting productivity and innovation. Companies can more easily find specialized suppliers and skilled workers, and collaborate with other firms. This concentration often leads to higher wages and more diverse job opportunities.

Environmental Sustainability: This improves significantly with density. Per capita energy consumption typically drops as people live in smaller spaces and share walls, reducing heating and cooling needs. Public transportation becomes more viable and efficient when serving concentrated populations. Car dependency decreases as destinations become walkable, reducing emissions per person. Dense cities have much smaller carbon footprints per resident than sprawling suburbs.

Infrastructure Cost-Effectiveness: The larger scale makes dense development financially attractive. Roads, utilities, schools, and public services cost far less per person to provide when populations are concentrated rather than spread out. A single subway line can serve hundreds of thousands of people efficiently.

Cultural Vibrancy: This flourishes in dense environments. Such areas support diverse restaurants, theaters, museums, music venues, and cultural institutions that wouldn’t be economically viable in less populated areas. The mixture of different communities, backgrounds, and ideas creates dynamic cultural scenes.

Convenience and Accessibility: Residents can often walk to work, shopping, entertainment, and services. This reduces time spent commuting and increases quality of life. Healthcare, education, and other essential services are typically more accessible and higher quality due to competition and specialization.

Innovation and Knowledge Sharing: These accelerate when creative people work in proximity. Many of history’s greatest innovations have emerged from dense urban environments where ideas cross-pollinate rapidly.

Preservation of Natural Areas: When more people live compactly, larger areas of countryside and wilderness are left undeveloped.

A “woonerf” street in the Netherlands, via Nature’s Path.

But how dense is dense? “Urban density” refers to the measurement of population, housing, or development concentration within a given urban area and is typically expressed in several ways.

Population Density: This is the most common measure, calculated as the number of people per unit area (usually square kilometer or square mile). For example, Manhattan has about 70,000 people per square mile, while typical suburban areas might have 500 people per square mile.

Housing Density: This measures the number of dwelling units per unit area (often, hectare or acre), a number that helps urban planners understand residential concentration regardless of household size variations.

Built Density or Floor Area Ratio (FAR): A real estate metric that measures the total floor space of buildings relative to the land area they occupy. A FAR of 2.0 means a building’s total floor space is twice the lot size, which could be achieved with a two-story building covering the entire lot or a four-story building covering half the lot.

Urban density exists on a spectrum from low-density suburban development (single-family homes with large lots) through medium-density areas (townhouses, low-rise apartments) to high-density urban cores (tall towers as well as low-rise, high-density housing). Different cities and neighborhoods can have vastly different density patterns while still being considered “urban.” The definition matters significantly for urban planning, as different density levels support different transportation systems, commercial viability, and infrastructure requirements. Understanding density helps planners make decisions about zoning, public services, and development policies.

There is a common assumption that tall buildings mean more density, but it’s not always so. Many of the high-rise developments built by the New York City Housing Authority (NYCHA) in the 1950s were relatively low-density. The overcrowded tenement housing in lower Manhattan packed people in at 1,100 people per acre in buildings that were only four or five stories tall. In response to these conditions, the 1901 Tenement House Law required new housing to have larger lot sizes, courtyards, and better amenities like plumbing and running water. Later, the “garden apartments” of places like Jackson Heights dropped density to 155 people per acre. When the NYCHA began its federally funded “towers-in-the-park” developments in the postwar years, it achieved densities of less than 300 people per acre, even with buildings as tall as 30 stories, due to the low site coverage. Even the 15-story buildings of Stuyvesant Town achieved only 302 people per acre. 

An exhibition and publication by the Skyscraper Museum examined the question of housing density and found that: “The Depression brought government funding into the business of housing, and by the 1950s ‘towers in the park’ became the standard approach to slum clearance and urban renewal. Yet this formula for working- and middle-class projects, which were designed at extremely low density, housed far fewer residents than the tenement blocks they replaced.”

So we can see that it’s a mistake to automatically equate tall buildings with high density. In the 1960s and ’70s, New York planners began to favor “low rise, high density” over tower-in-the-park typologies and as an alternative to the low-density suburban development that had been popular in the postwar years. “Low rise” typically means no more than four or five stories, and “high density” typically means at least 55 units per acre, denser than many NYCHA high-rise projects. “Low rise, high density” also makes for more walkable neighborhoods and is environmentally beneficial compared with low-density suburban development, which uses copious amounts of land and creates traffic.

Another feature of “low rise, high density” is that these designs generally follow the “street wall” rather than set back from the sidewalk, restoring some of the typical street feel common to the city. At four stories or less, these buildings can also save on the cost and maintenance problems of elevators. In the U.K., zoning has encouraged the development of low-rise, high-density housing, and there are many fine examples of that typology.

But how much density do we need to support services like local retail, transit, schools, health care, and so on? What is the “perfect density” for urban living?

Density varies widely between rural areas and urban areas. In the U.K.’s Lake District, which I often visit, the density is 44 people per square mile (sheep density is considerably higher). It’s beautiful, but try finding a carton of milk after 5:00 p.m. Sullivan County (N.Y.), where I also spend time, runs at around 96 people per square mile. You definitely need a car there.

Low-density suburbs typically run around 500 people per square mile; Palo Alto, California, jumps to 2,650, and Staten Island, 8,112. I’m sure all these places are loved by their inhabitants, but are they sustainable in terms of delivering the “15-minute city” level of services without car dependence?

A common benchmark to support diverse retail and services is 10,000 people per square mile. There also appears to be a correlation between population size and amount of retail square footage (see this 2019 study by Cushman & Wakefield). Park Slope, in Brooklyn, weighs in at 45,000 people per square mile, Manhattan at 72,918. They seem to me to set a reasonable benchmark. You might not favor Manhattan’s density, but you probably don’t want to drop below Park Slope’s if you want to support the transit, restaurant, and cultural choices you need. (Dhaka in Bangladesh, however, at 440,000 people per square mile, might just be taking it too far.)

In New York City, the recent City of Yes (COYHO) legislation and proposed charter revisions aim to improve housing supply, and thus, it is hoped, affordability by increasing the allowable density in specific areas that have historically had density zoning restrictions but offer infrastructure that could support higher density.

Outside of the business districts of Manhattan, Brooklyn, and Long Island City, New York is fairly flat—block upon block of terraced housing, most of it less than four stories.

COYHO was passed in December 2024 and divides New York into three types of districts: low, medium, and high density. To encourage development in low-density districts, it permits buildings of three to five stories within 1.2 miles of a transit stop, and apartments above commercial buildings. It also permits “accessory dwellings,” add-ons to existing one- and two-family homes. In medium -and high-density districts, developers can add 20% more units if the units are affordable to households earning up to 60% of the median income. COYHO also significantly reduces parking mandates that really should be a relic of the Robert Moses era. Sadly, it stopped short and allows such mandates in the outer boroughs.

There is much to criticize in COYHO, as I have discussed in a previous Common Edge essay. It looks more like a giveaway to private developers than a social housing program. But even if it does not solve the affordable housing crisis, there is something to be gained by the modest increase in density that the policy hopes to promote.

The New York City Mayor’s Charter Revision Commission drafted a series of changes to streamline and speed up how the city approves new housing projects. Some are controversial in that they diminish the role of city council members in land use decisions. The ballot proposals that will be before the voters this November include several that affect density. Proposal #2 includes expedited review for housing projects in the 12 community districts with the lowest rates of affordable housing. This process would allow the community board and local borough president to review at the same time, followed by a 30- to 45-day review by the City Planning Commission, which would have final approval instead of the City Council.

It seems like a good idea to reduce ”member preference” and the NIMBYism that has prevented affordable housing in certain neighborhoods that strive to maintain lower density. I wish the CPC were more independent and not just a tool of the Planning Department and the mayor.

Proposal #4 establishes an Affordable Housing Appeals Board with the council speaker, local borough president, and mayor to review council actions that reject or change applications creating affordable housing. This seriously reduces the City Council’s involvement and is probably aimed at the “member preference” problem. It is an awful lot of power to put in the hands of three people—a throwback to the old, unconstitutional Board of Estimate.

There is a lot to be concerned about with both COYHO and the ballot proposals, but density is not among them. As the world urbanizes, we need densities of at least 45,000 people per square mile (sorry, Staten Island) in order to maintain the services, public transit, retail, healthcare, education, and culture within a sustainable distance that does not require driving or using up acres of land.

As cities grow—and the prediction is that half the world population will live in cities by 2050, with 67 cities exceeding 10 million people—we need “15-minute cities,” not suburban highways and shopping malls. As planners, we need to rebrand city density as a quality-of-life benefit, not a dystopian threat.

Featured image via Reddit, r/CityPorn.