Mapping the track of underground cables is not easy. However at present, there is a good opportunity to map the track of the cable of HVDC Kontek ( https://en.wikipedia.org/wiki/Kontek ), as one can read on https://www.50hertz.com/Portals/1/Images/Presse/50Hertz_Flyer_Interkonnektor_Kontek.pdf?ver=2020-04-17-163836-167 the cable is exchanged by a new cable in great proximity of the old one. So earth works take place, which can be easily mapped!