[Inkscape-user] Trace Bitmap - question

Hi,

I try to vectorise the outlines of a simple map, using "Trace Bitmap".

The bitmap has 2 colors - white background and a 1px black line for the outlines.

When I use "Trace Bitmap", I get a path on both sides of the black line - but I want just one in the middle of the black line. See: http://www.hagoschaos.de/h/freunde/karteG.html

Is there a way?

Hago