A surface for a 2D top-down game

I’d like to make a 2D top-down game.
To do that, I’ll need a surface the characters will walk on…
I saw that I can use a lot of square sprites and use them to build a larger square (n*n matrix of little squares)
But I prefer to use a single large object.
Is it possible?
Can I define a sprite to be as big as I want?
Or should I use an Image from the UI objects?

Yeah, go for it. Doesn’t really matter if you use a large sprite/image or not. You can change the size with the Scale property.