WWNA Aguada PR 1340 - How To Make A Coverage Map

In October 2013, I was lucky enough to hear, and confirm, WWNA Radio Una 1340 AM from Aguada, PR. The confirmation was in fact machine-translated into Norwegian. This afternoon, to my surprise WWNA sent a coverage map. In my early days of DX-ing, coverage maps were often received from North American radio stations. None of them were anywhere near as beautiful as this one, so I thought I'd share it.