Jax: The map is 2000 pixels square. Since the pixel dimensions are fixed, then dpi makes no difference, as that is only metadata. I can make a 2000 pixel square image at 10 dpi or at 1,000 dpi, and the file size will be exactly the same. The only things that will change are the size it prints out on paper and what Photoshop might do when you tell it to zoom to 100% (there's a setting in there somewhere that determines whether you see 1:1 pixels or 1:1 inches. The default is to show the pixels, which minimizes distortion from resampling.)

I suspect that Clercon is correct, and that the image is being worked in a deep color space. I would add a caveat, though, that there is usually no need to work at greater than 8-bit, but sometimes the extra precision of 16-bit mode is helpful for height maps, and 32-bit mode can make color operations almost non-destructive. If you don't have a specific reason for needing that extra precision, though, then stick with 8-bit.