Dune Sand - Object based image analysis for vectorization of a dotted signature in Danish late 1800s maps

The geography and history of the 300 km coastal zone of western Jutland is marked by the role of dune sand.Tides, currents and waves deposit marine sand as beaches. During low water, the prevailing winds and frequent storms drive the beach sand inland. For much of this coast, a zone of high dunes forms a natural coastal de-fence, backed by several kilometres of landscapes of windblown sand, which are Denmark’s main semi-naturalwilderness areas. These have experienced widespread modern era changes, with establishment of plantationforests and holiday homes. Documentation of the changes and analysis of their effects requires digital geo-data of the former extents of the dune sand. The Danish Høje Målebordblade (HMB) set of historical mapssurveyed from 1870-1899 record the earlier distribution of dune sand. In these maps, dune sand is signatured as fine black or dark grey dots with a relatively even spacing. The dune sand signature itself has no colouration,but dune sand dots locally overlay the colourations applied for the HMB heath and wetland legend items. Ademonstration project of the possibilities for automated vectorization to digital geo-data of HMB map landcategories has had dune sand as one of its target classes. Automated mapping of dune sand has involved useof a sequence of object-based image analysis methods, including use of a raster of the distance to each dot.The resulting dune sand vector layer, for a 200 km2 coastal test area in NW Jutland has, assessed against a 100m spaced set of control points, a false-negative rate of under 5% and a false-positive rate of around 10%