I have an image map with many thousands of coordinates plotted. I need to make the actual image smaller, which means all the coordinates will need to change. It would take literally days to go through a manually plot the coordinates, so really I need another method. Has anyone faced this situation before, and if so, how did you tackle it?

I know this could be achieved by simply multiplying the coordinates by, for example, 0.5 if the image is half as wide and half as high, then rounding the number produced to an integer. I'm sure this is something that could easily be done with PHP, but I couldn't find anything on a Google search. I could write this script myself, but would ideally like a quicker solution as I'm sure it must already have been done somewhere.