Nick,

Caret stores curvature, depth, or thickness data in a shape file. In the example caret gifti data files, the shape files have the "*.shape.gii" filename extension.

The advantage of storing shape related data in a file separate from the surface is that it allows the display of one copy of the shape on multiple surfaces. For instance, even though the shape data is normally computed on the anatomical surface, displaying something such as curvature on an inflated and especially a flat surface is helpful.

John Harwell