Well, I've just received my ILI9488 and a couple more ESP32 modules so I'll be putting those together.(We're not leaving Andy anything to do )
That's the way I did it; using an on-line polynomial fitter to generate the equation only I used
The query I raised in the 'bugs' section about slow write speeds on an ESP32 is a bit of a bother as well. Not a problem when all is up and running but during debugging I was corrupting my history file if I forgot to wait a minute or so after a re-run for the write to complete. I'm wondering if the same problem would occur using FILE.SAVE_IOBUFF to save the data in one hit rather than as discrete writes.
There is a slight difference in my map in that I shifted the x axis a couple of hundred miles to give New Zealand a bit of breathing space and to stop Hawaii being right on the 'fold' of the map as these places do see a lot of seismic activity. (Isn't that the way when you're using a paper map; The place you're interested in is either on the fold or right on the edge )
The thing about map projections is there are so many to choose from (although only a couple which you can sensibly put on an LCD screen). I did try it with an equirectangular projection which would have made both the X and Y axes linear but Africa and the Americas were so stretched from what we're used to seeing that it didn't look 'right'.