It would be handy to be able to display geographical coordinates as a HUD text, similar to coordinate display in traditional minimap mods.

Hello, thank you for your request.
This is definitely doable and could be implemented quite easily, but I'm too busy with other stuff to work on Terramap right now.
I'm adding it to my TODO list over on Trello.

On the mean time, you have two similar features you could use:

• The latitude and longitude are visible on the F3 debug screen
• You can assign a key to copy them directly to your keyboards in the Minecraft control menu

Hope that helps.