procedural path painting on terrain

This works and works great except when i pull gps coordinates into unity world coordinates they are floats and setalphamaps only take ints which lat 43, lon 71 and lat 44, lon 72 are VERY far apart gps wise. I am not sure what to do there. Any ideas would be great.

I considered making a terrain the max size of a float(3,5) which would be 1 meter = 1 unity unit but can only make a terrain max size 100k