HotPads.com provides interesting heat maps. I am not sure how accurate it is but the service looks very promising, especially if you are looking to rent or buy in certain area.
Above is a heat map of household income of San Francisco. The meter stops at about $61K, I wish it went further to something like $200-300K at least.
HotPads, which brought us the foreclose heat map, now offers a handy rent ratio heat map. The rent ratio is a home’s sale price divided by the annual rent of a comparable home in the same neighborhood. Looking at the rent ratio gives you a quick sense of whether it makes more sense to rent or buy in a particular neighborhood. If the ratio is high (red on the map), it is usually a good indication that you are better off renting. If it is low (blue on the map), you are better off buying.