Cities don’t appear randomly on a map. Their locations trace back to a handful of powerful forces: access to water, defensible terrain, natural resources, and connections to trade routes. Growth, once a city is established, depends on a different but overlapping set of factors, from transportation networks and economic opportunity to government policy and, increasingly, digital connectivity. Understanding these forces explains why some places become megacities while others remain small towns.
Site: The Physical Features That Start a City
In geography, a city’s “site” refers to the physical characteristics of the land it sits on: the terrain, climate, soil quality, and natural resources available. These features determine whether building infrastructure is even feasible and whether a population can sustain itself. Flat, well-drained land near fresh water has always been the most attractive starting point. River valleys, coastal plains, and lakeshores account for the locations of most of the world’s oldest cities.
Climate plays an equally fundamental role. Mild temperatures and reliable rainfall support agriculture, which historically needed to exist nearby to feed a growing population. Extreme cold, arid deserts, and dense tropical forests all slow urban development, though technology has gradually reduced these barriers. Phoenix and Dubai exist as major cities today because air conditioning, desalination, and long-distance water systems made them livable, but their growth came centuries after cities in more temperate zones.
Why So Many Cities Sit on Rivers
Water access is arguably the single most important factor in city placement throughout history. Rivers provided drinking water, irrigation for crops, a power source for mills, and a transportation highway for moving goods. In North America, the pattern is strikingly visible along what geographers call the “fall line,” a geological boundary where rivers drop from rocky highlands to the softer coastal plain.
European settlers sailing up rivers from the Atlantic coast would hit impassable rapids or waterfalls at this line and could go no further. So they unloaded their ships and built settlements right there. These spots had a double advantage: they were the furthest point inland that ocean-going trade ships could reach, and the falling water provided energy to power mills for grinding grain, processing cotton, and producing steel. As of 2020, the first or second most populous cities in six US states sit along this fall line. Philadelphia, Richmond, Raleigh, and Columbia all owe their locations to this geological feature.
Situation: Location Relative to Everything Else
While site explains the ground a city sits on, “situation” describes its position relative to other places. A city with a perfect site but no connections to trade routes or neighboring populations will struggle to grow. Situation encompasses proximity to other cities, access to markets, and the transportation routes linking them all together.
This is why port cities have historically dominated global population rankings. A deep natural harbor connected a city to international trade, and that trade attracted merchants, laborers, and wealth. New York, London, Shanghai, and Tokyo all grew enormous partly because their harbors positioned them as gateways between inland economies and global shipping lanes. Inland cities that thrived, like Chicago or Moscow, typically sat at the intersection of multiple transportation corridors, whether rivers, railroads, or highways.
Transportation infrastructure reshapes situation over time. A city that was poorly connected can vault into prominence when a new rail line, highway, or airport links it to larger markets. Atlanta’s explosive growth in the twentieth century owes much to its position as a railroad hub and later as home to the world’s busiest airport. The construction of the Interstate Highway System in the 1950s and 1960s similarly redirected growth toward cities with major interchanges and away from towns the highways bypassed.
Natural Resources as Growth Engines
The discovery of valuable natural resources has launched cities into rapid growth, sometimes almost overnight. Coal, iron, oil, and natural gas have each created urban centers built around extraction and processing. Baku, Azerbaijan grew into a major city through oil and gas extraction. Aberdeen, Scotland became the energy capital of Europe’s North Sea oil industry. Calgary and Houston both rose to prominence on the back of petroleum economies.
Resource-based cities face a particular vulnerability, though. When the resource declines or global prices crash, these cities can hollow out. Ordos, China, built on coal and natural gas wealth, now faces high rates of idle urban land, excess commercial buildings, numerous unfinished construction projects, and population loss. The cities that survive resource transitions are the ones that diversify. Houston has shifted heavily into aerospace, medicine, technology, and business services. Calgary has expanded into financial services, digital media, and life sciences. Aberdeen has added life sciences and technology alongside its energy sector.
Universities and the Pull of Human Capital
In the modern economy, educated workers matter as much as physical resources. Cities with major research universities benefit from a powerful economic multiplier: every dollar increase in university spending has been shown to produce an 89-cent increase in average income within the city. The overall multiplier effect of university activity is 1.9, meaning each dollar the university spends generates nearly another full dollar in the surrounding economy.
Universities located in downtown urban areas are especially potent growth engines. They produce 80 percent more licensing deals, 123 percent more patents, 222 percent more income from licensing deals, and 71 percent more new businesses compared to their rural, suburban, and college-town counterparts, according to Brookings Institution research. This helps explain why cities like Boston, San Francisco, and Austin have grown rapidly in the knowledge economy. The university acts as a magnet, attracting young, educated workers who then start businesses, fill skilled positions, and draw further investment.
Government Policy and Political Power
Capital cities grow partly because governments concentrate jobs, spending, and infrastructure investment in them. Washington, D.C., Brasília, and Canberra all exist primarily because political decisions placed national capitals there. Zoning laws, tax incentives, and housing regulations also shape which cities grow and which stagnate. A city that makes it easy to build new housing can absorb population growth; one that restricts construction pushes people elsewhere.
Special economic zones and tax incentives have redirected growth in dramatic ways. Shenzhen, China transformed from a fishing village to a city of over 17 million people in roughly four decades, largely because the Chinese government designated it a special economic zone in 1980. On a smaller scale, state tax policies in the US have contributed to migration from high-tax states toward cities in Texas, Florida, and Tennessee.
How Remote Work Is Reshaping City Geography
For most of urban history, people had to live near their workplace, which meant living in or near a city center. Remote work is loosening that constraint in measurable ways. Before the pandemic, only about 5 percent of work days in the United States happened at home. That figure spiked to 60 percent in mid-2020 and has since stabilized at nearly 30 percent of all work days.
The effects on cities are concrete and persistent. City centers in the top 12 US cities experienced cumulative net population outflows of 8 percent compared to their 2019 levels. Spending in city centers has dropped roughly 15 percentage points relative to surrounding suburban areas, a gap that stabilized in 2023 rather than recovering. Home values tell a similar story: prices in high-density city centers and suburbs diverged by over 40 percentage points by September 2023, with suburban values climbing far faster.
Cities with the highest rates of remote work saw the biggest changes. The top third of cities by remote work adoption experienced population outflows from their centers that were 5 percentage points greater than from their outskirts. The bottom third saw almost no difference, just 0.5 percentage points. What this means in practice is that remote work weakens the forces pulling people into dense downtown cores but preserves the broader appeal of metropolitan areas. People are spreading out within metro regions rather than abandoning them entirely.
Climate and Environmental Limits
Environmental factors have always constrained where cities can exist, but climate change is actively redrawing those boundaries. Rising sea levels threaten coastal cities that were founded precisely because of their waterfront access. In the US alone, an estimated 13 million people could be forced to relocate due to rising seas by 2100. Six feet of ocean-level rise would redraw the coastlines of southern Florida, parts of North Carolina and Virginia, and most of Boston and New Orleans.
This migration won’t happen all at once, but it will redirect growth. Inland cities at higher elevations stand to gain population, while low-lying coastal areas face declining property values and eventual abandonment of some neighborhoods. Cities in wildfire-prone areas, extreme heat zones, and drought regions face similar pressures. The places that grow fastest over the next century will likely be the ones that combine economic opportunity with relative climate safety, a factor that barely registered in urban planning a generation ago but increasingly drives where people choose to live.