When you’re traveling it can often be difficult to know exactly whether it’s your fault you have no signal or if there is simply no cell towers or Wifis within range. There’s a very cool little app called Architecture of Radio that can help.
You can’t see in the picture, but as you turn you can see the various radio towers, their relative signal strength, approximate distance, who owns them and various other facts. You can even see the geo-stationary satellites in orbit.
There are some places I go that have very poor signals, and it was easy to see which carriers were close by and which ones would have a better signal strength, simply by turning around. It’s a fun party trick, but also very useful for knowing where you need to head to get a stronger signal.