Turns out implementing yards instead of pixels was ridiculously easy. It took one global constant and applying it in a few places.
As a bonus, I also figured out how to easily resize the .bmp’s in windows, which I have done.
First things first: the field is 100 yards by 100 yards, which is obviously ridiculous. Also, the players are now probably too small, since they are 5 x 5 images, and the resolution is set at 800×800, which makes them 0.625 yards x 0.625 yards.
Still, those are minor problems and the media is meant to be thrown away later.
Edit: One really irritating thing is that wordpress keeps resizing my .png’s, which would be fine if you could click on them and see their natural size, but you can’t.