Comprehensive topographic and geographic recordings of countries by surveying and by cartographic representation in (official) map series at different scales emerged in the late 18th century as precursors of the nowadays used topographic maps. For spatio-temporal working disciplines the scanning and georeferencing of older topographic maps is of great importance to study landscape changes over long periods of time. In the DFG project »Virtuelles Kartenforum 2.0« more than 6,000 scanned topographic maps at a scale of 1:25,000 in the borders of the former Deutsches Reich are georeferenced and disseminated as WebMapServices (WMS). For the step of georeferencing the huge amount of maps, a crowdsourcing approach is presented in this paper. The results achieved are studied in terms of data quality.