Two maps can be quite different even if their average quantization and/or topological errors are equal. Therefore a measure of similarity between maps would be useful. Similarity could be based on comparing the location of BMUs of input vectors on two different maps . This is however sensitive to the size and orientation of the map.
A much better measure was proposed by Kaski and Lagus . The method is an extension of the topological quantization error presented in previous section. The shortest paths between each sample vector pair and going through their BMUs i and j, respectively, are measured on both maps and :
where k' is treated in the same way as in 3.5. The dissimilarity between two maps is taken as the expectation value of the relative absolute difference of these distances: