Last summer, we drove from Seattle to Minneapolis, in a meandering way. There were plenty of times that I had no coverage, period, because I am an AT&T subscriber with a phone that will not function on Verizon’s network. There were plenty of times when my iPhone showed that I had a data signal, but I did not. And there were plenty of times when all I had was voice, no data.
What other things might the map be hiding? The cost (for example, taxes on mobile service) perhaps?