KP13hj is the grid square, calculated from the position of my home station Jeppo Tower OH6LEI. Described on the net: "The resulting code is sent as two letters (field), followed by two numbers (square) and optionally two more letters (subsquare). For instance, (0°N, 0°W) would be abbreviated as JJ00aa"
Now days with Google Earth Maps, your house can be spotted with an accuracy of some meters.