So you say "most software won't do this....". What software do you use that generates a spread map like your 2nd map shown? 

Are you suggesting a particular software? Or just saying that some mapping systems can already make such spread maps? I'm interested.

After spreading our own VRT fertilizer for a few years now, I understand that a custom spreader going 18 ++ mph can't possibly keep up with the changes per the grid, zone, or whatever.....accurately.