A method of determining a longitudinal position of a vehicle (100) relative to a digital map is disclosed in which real time scan data (200, 202) is determined by scanning a lateral environment around the vehicle using at least one range-finder sensor, said real time scan data comprising one or more depth maps, each depth map representing the measured lateral distance to surfaces in the lateral environment for a plurality of longitudinal positions and elevations. Localization reference data associated with the digital map for a deemed current longitudinal position of the vehicle (100) in relation to the digital map is retrieved, and compared to the real time scan data (200, 202) by calculating a cross-correlation to determine a longitudinal offset. The deemed current longitudinal position is adjusted based on said longitudinal offset to determine the longitudinal position of the vehicle (100) relative to the digital map.