Most of my hex game maps are also 641x641 pixels. They almost exclusively use the flat-top hex orientation, and are generally 23 hexes wide by 21 hexes high, with a surrounding "Off Screen" blank border, like this:
I've also elected to use the common hex numbering system as represented by e.g. Worldographer RPG Map Software, as seen here:
except that, because my maps are only 23x21 hexes, I just use four-digit rather than six-digit numbers, seen here as blown up ten times:
For details on how I laid out this hex grid, and how I surmounted some difficulties with precision, please see my Stellar System Thoughts - Page 9 herein.
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M.D.J. 2022/08/27