working on drilling is 'dreadfully boring' ....was the pun intended?
Welcome to the Guild, DG, Gimp is a great (free) tool, but also check out Inkscape which is also free but a vector based application. Many people prefer to use Inkscape for labelling maps (much faster) after they have drawn them in gimp. If you're after mapping a city, vector can often be more compatible (depending on your workflow and what you want to achieve).
Enjoy your stay here!