Converting the legend of the Soil Map of Belgium into the World Reference Base for Soil Resources: Strenght and constraints of using WRB as a map legend

Within the European Union, there is a general interest to prepare joint soil maps at a 1:250000
scale in order to harmonise agricultural and environmental policies. The World Reference Base for
Soil Resources (WRB) has been adopted as the common soil classification system within the EU.
As soil surveys in most member states were conducted independently, the challenge is now to
convert the national legends into a common WRB legend. Based on our experiences from
converting the legend of the Soil Map of Belgium to WRB, we discuss the strengths and constraints
of using WRB for both large scale (1:50000) and small scale (1:250000) maps. By using WRB
Reference Soil Groups with one or two main qualifiers, the principal soil information of the original
1:20000 scale Soil Map of Belgium can be represented. Inevitably the conversion to WRB leads to
some loss of information as details on soil texture, drainage and substratum get generalised into
broader categories in WRB. This generalisation however can be neatly presented on 1:50000
scale maps. Being less complex than the original maps, these maps have the advantage to
provide better insights into the regional soil geography. Moreover, as they are built on international
classification concepts, the historical soil maps are made accessible to a wider audience. The
conversion into WRB units also allowed for a straightforward generalisation and production of small
scale maps (1:250000) which should be suitable for producing a soil map at European level.