The reliability of indicator values depends on a number of factors. Most relevant is certainly the precision of input data, particularly that of the ATKIS Basis-DLM. The number of geo objects (at a spatial precision of 3 m) corresponds with the content of topographic maps at scales 1: 10,000 to 1: 25,000.
The semantic precision of geo base data also plays an important role in the classification and correct attribution of geo objects. Data errors and gaps are successively corrected by the surveying authorities. Indicator values calculated by the various states (particularly for built-up areas) can show systematic discrepancies due to variations in the interpretation of data capture guidelines (ATKIS object type catalogue).
In general we can say the indicator values become more reliable with increasing level of spatial aggregation, i.e. when spatial units increase in size this tends to counterbalance the effect of local errors.