A method, performed by at least one apparatus, the method comprising: - obtaining sample measurements at least in part comprising altitude information and observed in an area at least in part represented by an altitude map , the altitude map comprising sub-sections representing respective sub-areas of the area and comprising one or more altitude values for at least some of the sub-sections; - determining altitude estimates from the altitude information, wherein the determining of the altitude estimates comprises correcting the altitude estimates based on altitude values of single level sub-sections of the altitude map; - updating one or more altitude estimate distributions associated with respective sub-sections of the altitude map based on the determined altitude estimates; - determining , for one or more sub-sections of the altitude map, whether a respective sub-section of the altitude map represents a single level sub-area or multilevel sub-area, based on respective altitude estimate distributions associated with respective sub-sections of the altitude map; - in case a sub-section of the altitude map represents the single level sub-area, determining a single altitude value based on the altitude estimate distribution associated with the respective sub-section of the altitude map to be used as the altitude value for the respective sub-section of the altitude map; - in case a sub-section of the altitude map represents the multilevel sub-area, determining multiple altitude values based on the altitude estimate distribution associated with the respective sub-section of the altitude map to be used as the altitude values for the respective sub-section of the altitude map; and - updating the altitude map with altitude values determined based on the altitude estimate distributions. - obtaining sample measurements at least in part comprising altitude information and observed in an area at least in part represented by an altitude map , the altitude map comprising sub-sections representing respective sub-areas of the area and comprising one or more altitude values for at least some of the sub-sections; - determining altitude estimates from the altitude information, wherein the determining of the altitude estimates comprises correcting the altitude estimates based on altitude values of single level sub-sections of the altitude map; - updating one or more altitude estimate distributions associated with respective sub-sections of the altitude map based on the determined altitude estimates; - determining , for one or more sub-sections of the altitude map, whether a respective sub-section of the altitude map represents a single level sub-area or multilevel sub-area, based on respective altitude estimate distributions associated with respective sub-sections of the altitude map; - in case a sub-section of the altitude map represents the single level sub-area, determining a single altitude value based on the altitude estimate distribution associated with the respective sub-section of the altitude map to be used as the altitude value for the respective sub-section of the altitude map; - in case a sub-section of the altitude map represents the multilevel sub-area, determining multiple altitude values based on the altitude estimate distribution associated with the respective sub-section of the altitude map to be used as the altitude values for the respective sub-section of the altitude map; and - updating the altitude map with altitude values determined based on the altitude estimate distributions. <EOS>