Though in heavily dense areas that have different commutable neighborhoods this can still be off. In NYC you have commuters from New Jersey, Connecticut, the various Borroughs and even upstate NY or Pennsylvania. Each of these will have a vast difference in average rents within their community - for example, my rent in Staten Island for a comparable place within any of the other Burroughs will be a lot lower because I am willing to trade in commute time for it, even though my salary will be comparable to other developers within NYC.