What this means in practice is that nobody in San Francisco lives more than walking distance from an area of the city in which people are routinely mugged, whereas you have to get north of the 140s in NYC to see drastically increased crime.

San Francisco is, for its population, anomalously small. That plays into a lot of the problems perceive in it: it drives housing costs, makes transportation infrastructure harder to build, retards home ownership (and thus neighborhoods --- had a block party lately?), puts people into closer contact with crime, &c &c.

I lived in SF for several years, and I think 'potatolicious is if anything understating his case.