Positioning locations on the map

So the problems are falling one at a time on this - (1) have learned how to draw a map (or any image, for that matter) to the window, (2) have acquired a list of all of the districts in TX (all of the schools, for that matter, which I was able to parse down to a list of districts), (3) have figured out how to convert the addresses to longitude and latitude. Now the question is how to convert longitude and latitude to positions on the image - not a DIFFICULT problem, but one that took some thought. I think I worked it out during a long drive this weekend. Will try to implement tomorrow.