It most cases it makes more sense for a satellite operator to concentrate signals to a certain area on Earth, mainly that part of Earth where the intended recipients of tv, radio or data channels are at home. Fi, if the target audience is not at home on ships, it makes more sense to point a transmission antenna to land masses of Earth, than to oceans.
Most satellites have more than one antenna on- board.
It is therefore important to know which frequencies are connected to which transmission antenna in order to know at what parts of Earth signals can be received. For most of the satellites, SatcoDX has drawn the coverage areas towards where those antennas are beaming at. In center of those coverage areas reception is possible with smaller antennas than at edges of coverage areas. Outside coverage areas, reception is probably still possible, using more advanced equipment. The first three letters indicate satellite operator, the following three letters indicate type or version of satellite itself, and last two letters make a definition of individual antenna coverage area.