hi there is a game where a map consists of a .nif a .emr a .xml and various other small files, my question to anybody who knows is, what is the purpose of a xml and emr files thanks

The purpose is to store data.

What that data is, and how that data is interpreted depends on the game. It might be enemy positions, dialogue options, colour of the main character's socks, amount of bears in the castle, or whatever. It's impossible to say with such a generic question.

You're probably going to get better answers searching for that specific game, potentially also if you include mods in the search query.