Autotrace does have a tracing option "-centerline" which creates a single line on shape boudaries. I think it uses a fine thinning algorithm referenced in the scientific literature, but in the autotrace Todo list there is this item: "- Better thinning algorithm like CAT (Chordal Axis Transformation) " . http://autotrace.sourceforge.net/ https://github.com/autotrace/autotrace