Converting path/selection to single stroke?

[Ofnuts]

Wrong tool. There are paths/vectors in Gimp, but mostly to draw/delimit things. If paths are your main concern, use Inkscape.

I think what you mean is called "centerline".


See here for a way to obtain a single line from your bitmap, in particular the Autotrace software or the Inkscape "centerline" plugin.

If you remain with Gimp, you create paths by hand over your bitmap, this isn't that hard.