Bulgaria has a central axis along the Balkan Mountains, clearly aligned EW. This gives Bulgaria its square appearance. Comparing the mountainos region with convection cell model, it appears that they have drifted into the central axis enclosure of a row of polygons, therefore adjusted to a perfect EW alignment.
This divides Bulgaria into South and North parts. The coastal polygon is partly responsible for the formation of the Bosphorus.
As previously mentioned, this analysis was made on the occation of a visit to Kavarna with high cliffs at the seaside.