Define an outline with co-ordinates

I'm a newbie to this software and I've ran up against a problem I can't find a solution to. I have a very simple image, a white shape on a black background. I want to trace the outline of the shape and export the outline information as a series of evenly-spaced co-ordinate points. Any ideas about how I could achieve this? I thought perhaps a Macro would be the best way to go but didn't want to spend lots of time on it before I asked someone with more experience.

Cheers!