We talked before about measuring the amount of area within a map and we came up with a cool method which was really fast. I think the same can be applied to a length of path too.

If you create a new layer on top of the map and then draw with a known pixel width brush like 10 or 20 pixels wide in connecting solid lines - i.e. not dots - in black. Then once done you take the map layer and fill it solid white so that you have just a black and white image. No greyscale - contrast enhance 100% if you have to.

Now the nice feature PSP and Gimp has and I am sure PS has is this histogram window where if you hover your mouse in the histogram then it tells you how much as a percentage of the screen is white or black. So take number, multiply by image width x image height and that gives number of line pixels in image. Then divide by the 10 or 20 for the line width and that gives line length in pixels. Multiply by pixels per m scale and thats real length on map.

Rob did you ever Gimp up that area script ? If you did then its just area / 10 or 20 depending on the line width.