Hello, (I downloaded gsd/gsll a few days ago) In the documentation section 3.2.1 map-grid, the following example does not work: (map-grid :source 'index-fill-decadal :source-dims '(3 4)) Instead, it should probably include the `destination-specification': (map-grid :source #'index-fill-decadal :source-dims '(3 4) :destination-specification '((array 3 4) double-float)). The map-grid documentation is a bit unclear. It says that if `destination-specification' is not provided, map-grid defaults to `source'. But source is a function. Looking at map-n-grids code in map.lisp, I don't see a test clause that handles the case of unspecified `destination-specification' Mirko