A specialist repair shop may need customers from thousands of households to survive. A city brings enough people within reach for that service—and many others—to become possible. Nearby workplaces, schools, suppliers, and public spaces create opportunities that depend on density and connection.
Physical proximity alone is not enough. Transport, water systems, property arrangements, public safety, and the use of shared space determine whether people can benefit from being close to one another.
The same concentration creates costs
Agglomeration brings benefits alongside housing and living costs. A person may earn more in a large city yet spend much of the gain on rent and travel. Businesses can draw on a larger pool of skills while contributing to congestion and competition for space.
Cities also connect people unevenly. A neighborhood may be geographically near employment but poorly served by transit. A public square may exist without being welcoming or accessible to everyone. The map of buildings does not show the full map of opportunity.
Treating a city as a social technology means examining the arrangements that make proximity useful: how streets connect, how land is allocated, where third places let people meet, and who can remain as a place becomes desirable. Urban growth can create possibilities while displacing the people who helped create them.