Simpler area-based weighting for rasters in geographic coordinates

[dbaston]

It should be possible to use a flag to specify area-based weighting for rasters in geographic coordinates, rather than having to construct an input stack with previously-computed areas.

[helsharif]

Yes this enhancement would be greatly appreciated!

[dbaston]

I think this is sufficiently simplified by the ability to use weighting rasters with R summary functions, e.g., exact_extract(prec, brazil, function(x, cov, wt) weighted.mean(x, cov * wt), weights = area(prec)). At least, I'm doubtful that adding additional syntax would simplify a function that already has too many ways of calling it.