So for future reference, I think you’ll find that boolean actions are the way to go for dividing something like this.
There are lots of ways to do this – I’m using Inkscape here – but they boil down to the same process. It goes like this:
Get your map. (I took a chunk of Atlanta out of openstreetmap, exported as SVG and converted the roads to shapes, then combined them all into one mega map path)
Make your dividing shapes. I just made 4 rectangles and snapped them together:
Now align those rectangles on top of your map. I group the 4 rectangles, then used centering tools to align the group of rectangles to my map path.
Make 4 copies of that.
Ungroup and remove the rectangles that you don’t need.
Now select a map and an overlaid rectangle do an “intersection” in inkscape (it’s called something else in illustrator…)
And voila, you’re left with your map chunk.
Repeat with the other 3 quadrants… and you’re done, 4 neat chunks of your map.
It won’t speed up your cutting process, but your map division work will go to a matter of 1-2 minutes.