The previous ratings service, Asesores Inc., did the ratings Island wide also. In fact, PR has been a single market going back to the 50's, when TV started and it was set up for Island wide coverage out of San Juan. The Island is only 100 miles by 35, or no bigger than LA or other larger geographic areas. Terrain, not size of the geography, requires multiple simulcast signals. It takes 3 FM and 4 to 5 AMs to cover it all. Radio "networks" go back to the late 50's and 60's, and FMs FM networks (what in the US is called a simulcast) started in the late 70's, as FM became viable. Almost all the existing networks existed prior to Arbitron, and ALL of the major ones did. All the ratings, Asesores or Arbitron, allowed regional break-outs. Asesores provided San Juan, Northeast, SE, South, North and West. Arbitron allows custom areas in Maximiser, just like it does in every other Arbitron market.