I was in Stockholm for a few days this week and one of the things I thought about was the following: "Why does the US have so few real cities?"
The central city ins Stockholm has only about 600,000 people so it is relatively small. I stayed in Gamla Stan, the "old town" and the hotel I was in trances its roots back to the 17th century, so the city is old. Gamla Stan is also a small island; the city is actually a network of islands.
But what is it that makes a real city? First and foremost, there are alto of people walking around; a functioning mass transit system is probably a corollary to this characteristic. In addition to pedestrians and transit, Stockholm has a well developed bicycle route network and culture.
Aside
The Arland Express, the train to the airport, puts anything we have in NYC to shame. It leaves from the terminals and runs high speed to the city center in 20 minutes. The contrast with the Newark monorail and NJ Transit is stark; two badly marked trains, long wait in a post-industrial landscape and a slow, dingy train to Penn Station (which I admit does qualify as the city center).
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People live in real cities. Food is easy to find. There is retail at the street level and there are apartments above. There are museums and other cultural institutions. There is night life; that is everyone does not leave at the end of the work-day.
In the US clearly NYC qualifies. Boston probably does. San Francisco, DC and probably Chicago definitely do. LA, Raleigh and Miami don't
So what is my explanation? My guess is that the dominant explanatory variable is age. Real cities developed to a critical mass of people, housing stock and commerce before regular, long distance travel by people became common place; in particular before cars.
Aside
I recognize that cars are a relatively recent development, but so too is explosive population growth.
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A certain degree of geopgraphic constraint probably helps. Manhattan is an island, as is Gamla Stan and much of the rest of Stockholm. London is a counterfactual. "Transportation hub" and "seat of government" probably also help.