undistort projections as you zoom in

[ansis]

(related to the projections branch)

Different map projections are meaningful at lower zoom levels. At higher zoom levels they unnecessarily add distortion:

As you zoom in, we should transition to mercator to avoid distortion:

The transition should be gradual and should preserve the properties that are meaningful to that projection (not distorting area if it's equal-area, not distorting angles if it's conformal). It should be as subtle as possible and avoid jarring changes.

[ansis]

done in #10976