look at how my UTFGrid Data Interpreter page handles this:
if you view the page above without specifying parameters, there’s a little bit of description of iNat’s UTFGrid implementation. the last bit points to 2 references that i think are worth reading to help understand these a bit better:
A general primer for XYZ map tiles is available here: https://forum.inaturalist.org/t/in-pursuit-of-mappiness-part-1/21864#what-are-map-tiles-3. A good reference for UTFGrids is here: https://github.com/mapbox/utfgrid-spec/blob/master/1.2/utfgrid.md. It’s worth noting that UTFGrids are technically 64x64 grids, but the “Grid”-style map tiles in iNaturalist visualize data in 32x32 grids. So this page maps the data from the bottom-right cell from each 2x2 block of cells in the 64x64 UTFGrid to the corresponding 32x32 grid.
generally… the UTFGrid json file itself is composed of 3 parts – the grid, an array of keys, and the data object. to figure out what data is associated with any particular grid cell, you would translate the cell’s character to a numeric (index) value, then look in the keys array to find the key at the index value equal to the numeric value you just calculated. from there, you will look in the data object for the item with the key equal to the one you just retrieved.