Already when importing data into CadnaA - and this is exactly one mouse click onto the filename - many functionalities to optimize the data and the model can be used. The closed polygons presenting buildings in CadnaA are automatically produced even if the original data consist of many single lines as it is often the case with architectural drawings. Holes inside the building polygons representing backyards are treated correctly. Contour lines extremely detailed can be simplified reducing the number of points because such unnecessary details lengthen the calculation time without gain in accuracy.