Custom filled map

Hi everyone,

I want to use a filled map visual (or Azure map) but I can't figure out how to properly link my datas.
For exemple, I have an area called "01-est" as in "east of France" that will be assigned to Estonia.
So I want to know if I could create custom Json data to use in my filled maps (as with shape maps) or at least get to see what are the default layers.

Thank you !