This is a functional example, discussed in this page.
This was a code example provided while working as Technical Director for the release of Nelson Thornes Science eLearning product. Each module provided to the developers had a detailed 2 pages illustrative and technical pdf describing how the module would be expected to work. In this case it was simpler to provide the code than describe it in detail. The graphics are very basic.
The mobile phone can be dragged around the screen and the reception bars on each of the transmitter stations and on the mobile phone can be seen to change. The transmitter with the strongest strength is used by the phone. Grey areas are considered mountainous, when a user is on a mountainous region the reception is not affected, but being the other side of a mountain will shield the phone from signals on an opposing side. The end of the ariel is the reference point for signals.