In the config folder, there’s a fontlist.txt and a fonts.json.
Edit fonts.json so the final four entries look like this:
“overmap_fontwidth”: 16,
“overmap_fontheight”: 16,
“overmap_fontsize”: 16,
“overmap_typeface”: “square”
That changes the map so each character is 16 pixels wide, 16 pixels tall, using a font scaled for 16 pixels, and designed for looking good square. The “square” typeface seems to ship with C:DDA. If you want to use something else, consult the list of fonts in fontlist.txt and choose one of them by its name, not including the three letter acronym like .tff or .otf.
You may get weird results depending on what results you use, but the important bit is to make the overmap_fontheight and overmap_fontsize entries the same. You’ll also need to reload the game after you make any changes because the config files are read at start.