[perrygeo]

> simplify the data to lessen the load on the user's browser.

Yes, that's exactly the challenge. How DO you simplify/compress the data so as to convey the same information with less bits? That's effectively re-stating the fundamental problem of cartography.

Pragmatically, at web mercator z12, what features do you want to show? How about z14? An effective mapping service will dynamically provide the necessary data for a given zoom level, provided that you've defined "necessary" for each potential render.