Figure 7.

Areal distortion introduced by flattening. The figure shows the areal distortion produced when the right hemisphere was flattened in Figure 4. The original surface can be represented as a mesh of triangles. The areal distortion is a localized measure of the expansion or contraction of these triangles produced by the flattening operation. It is defined as ADi = log2(ASi/AFi) where i indexes a given triangle, ASi is its area in the original surface and AFi is its area in the flattened surface. In the figure, areal distortions tending towards black represent shrinkage, while those tending towards white represent expansions. One can see that the distortion is not uniform over the cortex, and it is greatest in regions with a high degree of curvature in the original image, like the frontal pole.