A district in San Francisco Bay is misclassified when applying the H - alpha decomposition. It is actually classified as an high entropy area, whereas this is expected to be of low entropy as it is an urban area. Among the differences between this district and the neighboring ones, we can quote the orientation of the streets and the inner organization. We use a 3D commercial tool (FEKO) to simulate an urban canyon in ideal conditions first and then for two types of geometric distortion. The analysis shows that these distortions may explain this high entropy observed for this particular district.