I’ve been searching for some time how I can change the fonts in my Linux cataclysm-tiles setup. As most Linux users will know, sometimes you won’t have a fonts.json file created along with your install (in my case /usr/share/cataclysm-dda), or even if there is a file or similarly named one called fontconfig.json, changing it has no effect.
I’ve recently found there area a series of files created under ~/.config/cataclysm-dda/ - including a fonts.json file. It only has three font options:
typeface
map_typeface
overmap_typeface
The default font is set as unifont, but changing the value here to any other monospace font installed on your system will alter the font used in game. As an example, I altered mine to:
{
"typeface": [ "Ubuntu Mono"
],
"map_typeface": "Ubuntu Mono",
"overmap_typeface": "Ubuntu Mono Bold"
}
You can also use fonts installed in the game directories /fonts folder (/usr/share/cataclysm-dda/fonts in my case).
Adjusting the size of the fonts is achieved in the in game settings under Settings -> Options -> Graphics.
For the typeface font, keeping the width/height ratio at 1:2 works fine. E.g, if you want to increase the font size to 22, the following settings work well for higher resolution and poor eyesight 
:
Font width: 11
Font height: 22
Font size: 22
The map fonts display the best when square (width & height the same).
Hope this helps someone in the future…was annoying me for a while not being able to change the fonts to something more aesthetically pleasing.