Is there a network mapping tool for path-loss?
What you're describing is known as a radio propagation model, which can range from very simple paper calculations (eg: free-space path loss, two-ray model, Hata models) to much more complicated software solutions which take digital elevation models as inputs and return path loss contours as outputs.

There are many propagation models in the second group, some of which can be quite specialized and expensive. The Longley-Rice model is probably the best known open-source model, and there are several free software implementations of it, such as SPLAT.