According to Google, downtown Houston is 1.84 square miles. Houston is 669 square miles. So downtown Houston represents about 0.3% of Houston. The reason it

According to Google, downtown Houston is 1.84 square miles. Houston is 669 square miles. So downtown Houston represents about 0.3% of Houston. The reason it is affordable in downtown Houston is because the other 99.7% of Houston exists, and if it weren't affordable in downtown people would just live elsewhere. You don't have the same choices in and around SF, therefore there is a lot of demand on much smaller amounts of land, therefore it's a lot more expensive! It's the same reason rent is really expensive in NYC, even though they are way more dense than SF. Lots of demand, not many alternatives.