I'm making a solo sandbox-esque campaign for my friend, the area of which is to be about the size of county (50 miles to a side). I was considering using gridpaper, with each square being a certain size, and detailing the contents of each square. I think a hexmap would be better.

She'll start near the center of the map, in her cottage home. She can explore and interact as she pleases. Each square contains certain terrain, structures, inhabitants, it's own set of random encounters (including one-time encounters, like the "hallowsprings griffon"), and any miscellaneous things I can think of.

Each square will be the same size, naturally, say, one mile to a side?

I might even make a map of each square, as I go.

Have any of you ever tried this or otherwise have any experience with this or something similar?