is it possible to get coordinates for image mapping without using image mapping software?

I am learning html/css and one thing that baffles me is the idea of image mapping, how am i suppose to get the coordinates of a section of an image and plug it into my area tag without using image mapping software like gimp. Using gimp's image map tool is really useful but I am concerned that i will need to know how to do this without gimp in the future for some special situation i can't think of, is there a way to get coordinates without image mapping software? Should i be concerned about relying on image mapping software?

thanks in advance!