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Data source: NOAA Great Lakes Bathymetry Tools used: R, with the {rayshader} and {magick} packages (magick is an R wrapper for imagemagick) Code: https://github.com/Pecners/great\_lakes\_bath As the subtitle calls out, the heights are exaggerated. I had trouble calculating the exact level of exaggeration, and I’d love to hear from GIS folks about how to do this. I set a scale of 50x, but that assumes equal spacing between x and y, and that the height is the same unit scale of x and y. So, I transformed the CRS to ESPG:3174, which I believe is 1 meter per degree. I checked this data too, and for the bounding box here, I calculated the width and height of the box (meters), and then divided by the degree difference of both (post-transformed, so used 3174), and I got 1 meter/degree for both width and height. Height is in meters, so that appears to work out. If I set scale to 1, it seems accurate, i.e. appearing flat, but this (with scale set to 50x) appears to be greater than 250x to me, because the deepest part of Lake Michigan appears to be as deep as it is wide there. That depth is around 280 meters, and the lake width there is at least 50 miles. For 280 meters to appear to be 50 miles, that scale works out to be 287x. Another possibility is that rayshader (or rgl which rayshader uses) is scaling differently than I understand it, but I reviewed the source code and couldn’t find an explanation.
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