An online system build a high definition map for geographical regions based on sensor data captured by a plurality of vehicles driving through the geographical regions. The high definition map comprises landmark map including representations of driving paths and landmarks and occupancy map comprising spatial 3D representation of the road and all physical objects around the road. The vehicles provide information to update the landmark map and the occupancy map to the online system. The vehicles detect map discrepancies based on differences in the surroundings observed using sensor data compared to the high definition map and send messages describing these map discrepancies to the online system. The online system ranks the vehicles based on factors including an upload rate of the vehicle and requests data describing high definition map from vehicles selected based on the ranking.