"Short distance between stops (due to low housing density)" If anything, you have it backwards. In most of SF, places with high housing density (e.g. Van Ness)

"Short distance between stops (due to low housing density)" If anything, you have it backwards. In most of SF, places with high housing density (e.g. Van Ness) have their stops closer together than places with far lower density (e.g. Geary in the outer Richmond). I suspect (but do not know for sure) that this is done on the theory that dense neighborhoods require more granular transit access.