I forgot to mention Lon/Lat.

I would suggest that be the predictors choice of:

1. Circle. Radius from a Lon/Lat pair.
2. Square. 2 Lon/Lat pairs of two opposite corners of the square.
3. Polygon. Formed by 3 or more Lon/Lat pairs.

This would allow the greatest flexibility for the predictor. Some like circles, Some like squares, and still others might want to make a parallelogram (spelling?) along a fault for example.

Thoughts?

-Michael