For many cities, not just NYC and SF, but yes, it is true only for major cities. EDIT: embellishment due to baq, this tends to be true of cities which develope

For many cities, not just NYC and SF, but yes, it is true only for major cities. EDIT: embellishment due to baq, this tends to be true of cities which developed before the car revolution of the 50's and 60's. For example, my city has a pretty poor average walkability score, but for where I live in the city core, it is very walkable since it is the older part of the city.