Is it possible to measure the distance of a WiFi access point from the receiver?
There are several research papers claiming that there is no correlation between signal strength and distance. I've read it - among others - on Radio Link Quality Estimation in Wireless Sensor Networks: a Survey by Baccour.

Now, I don't think this is true - there must be a correlation, otherwise you could in principle receive wifi signals from across the world. But it is demonstrated that this dependency is overwhelmed by other factors, such as the non-uniform radiation pattern of the antenna, multi-path propagation (highly significant due to the short wavelength), scattering and path loss due to obstacles.