A robotic work tool (100) comprising an altitude sensor (185) for providing a current altitude reading (HRL) and a controller (110) configured to receive the current altitude reading (HRL) from the altitude sensor (185)； determine an altitude (H) based on the current altitude reading (HRL)； determine a current position； and generating a map indicating elevations by including the determined altitude (H) for the current position in the map. A robotic work tool system (200) comprising a robotic work tool (100) and a reference altitude sensor (285) for providing a reference altitude reading (HCS), wherein the robotic work tool (100) is further configured to receive the reference altitude reading (HCS) from the reference altitude sensor (285)； and determine the altitude (H) based on the current altitude reading (HRL) and the reference altitude reading (HCS).
