UNCERTAINTIES OF COMPLETENESS MEASURES IN OPENSTREETMAP – A CASE STUDY FOR BUILDINGS IN A MEDIUM-SIZED GERMAN CITY

The completeness of buildings in OpenStreetMap (OSM) is estimated for a medium-sized German city and its surroundings by comparing the OSM data with data from an official building cadastre. As completeness measures we apply two unit-based methods that are frequently applied in similar studies. It is found that the estimation of OSM building completeness strongly differ between the methods. A count ratio (number of OSM buildings / number of reference buildings) tends to underestimate the actual building completeness and an area ratio (total OSM building area / total reference building area) instead tends to overestimate the completeness within the study area. It is argued that a simple pre-processing of the building footprint polygons leads to a more accurate completeness estimation when applying the count ratio. It is also suggested to more carefully examine the areas that have been mapped in OSM but not in the reference data set (false positives). In the present study region, these values are mainly due to simplified OSM polygons and they contribute to an overestimation of the OSM building completeness when applying the area ratio.