It depends on what your map units are. If the data is degrees, then the default is two degrees.
If the data is feet, the default is two feet. If your data is in meters, it would be unwise to grid
at one meter (you might want to file a bug report on that, since the utility would have to expect
to generate 750 *million* grid cells, and over 32k or so is too many). Frankly, the only sensible
default value would be the grid size of first level spatial index (gsize0).
- V