GIMP :: Digitizing / Tracing Image With 2.8 (2012)

I am considering using GIMP 2.8 on my system with Mac OS X 10.6.8 to do thefollowing:

(1) Digitise a photograph by tracing over parts of it with lines. The photocould be, say, the roots of a tree. The lines would be colour codeddepending on the state of what they are over. I.e. roots in one state getstraced with one colour, while roots in another state would get a differentcolour. In the end I might end up with a bunch of lines, with the differentcolours of lines organised in different layers.

(2) Calculate the relative proportion of lines of a certain colour to thetotal length of all lines.

To do the above, I am wondering if GIMP has the ability to calculate thelength of lines drawn over an image (in, say, number of pixels). This way, Ican obtain the total pixel length all lines put together, and the totalpixel length of, say, just the blue lines.

Do you think GIMP is suitable for this kind of image analyses? Or should Iuse a vector based program like Inkscape?