number of grid points, GRIBs and MapProjectionDisplay

Something is puzzling me re the visad.jmet.GRIBCoordinateSystem and the
MapProjectionDisplay example for display side coord systems...

Do Ni and Nj, in constructor params in the GRIB class, represent the
number of grid _points_ or the number of grid point _intervals_ ?? It
suggests the number of grid points, given the comments in the source code.

But if this is true, and it is the number of points and not intervals,
then would the range, and hence the defaultMapArea(), be 1,1,Ni,Nj and not

Otherwise the MapProjectionDisplay's adapter class, which maps lat/lons to
the display range -1 to 1, will be mapping row 0 to -1 and row Ni to 1.
Using this logic, the axis accommodates Ni + 1 grid points?

I'm sure there's an easy explanation, I just can't find it ;)