Wooden ring with 7 neighbouring areas
Wooden ring with 7 neighbouring areas of different colors. The allocation of the land is caused by a clover leaf sling and 7 bows of circles of latitude. a) The problem of the seven colors in the lattice plane as universal covering surface of Tours (392). The color cycle of the neighbouring areas around each land of 392 a is the same like on 392 with drawing.
Showcase of this model is Case number 28
Heawood, P.T.(1890). Quart.J.Math. 24, p. 332.