Each map is focused on one particular location of interest (hereafter referred to as the LOI) that has at some time in the past been a part of a mapping exercise. Some facilities have been used numerous times, so a large amount of data are available. Others have little or none. Markers are only shown for facilities with which communication with the LOI has been attempted, meaning at some point in at least one exercise there were operators at these pairs of locations transmitting and listening to each other.
Each map also applies for only one mode of communication to/from the LOI. It either shows (a) a Transmit Map, i.e., all facilities at which an operator attempted to receive a signal transmitted from the LOI, or (b) a Receive Map, all facilities whose transmissions the operator at the LOI attempted to receive. To state another way, a Transmit Map shows who can hear transmissions from the LOI, while a Receive Map shows who the LOI can hear.
Markers on the map are color coded to indicate whether a transmitted signal was heard, and contain a number reflecting the relative quality of the contact. A white marker with a "0" signifies that even though someone was listening at the given location, no discernable signal was detected. A shade of red indicates the signal was heard, with a darker shade (and higher number, maximum 5) reflecting stronger contacts. The green marker with no number shows the LOI.
The sample map below shows that when an operator at the LOI transmits it can be heard by several of the closer locations (red-shaded markers), but is not heard by some of the more distant ones and those where there are intervening hills. It also shows that the user can click on a marker to identify the facilities, or simply hover over the marker with the mouse.