radars just show detected objects(techs unless made to be difficult to detect) and the relationship of locations to the radar,
compasses show the magnetic/spin north and from that the ease south and west are estimated,
maps can show relationships between undetected but useful for navigation,
then there are GPS units that are basically a small computer with a compass and location system and map information, that display a map with location of the unit and other known(to the unit) information,
and adding a GPS to the radar would be great as you could see the map info locations and detected objects(other techs)
and in game I usually end up with 4 or five radars on my techs(usually from kills) so would prefer 1 radar short range and each extra radar adds 1/3 the single radar range to the detected range