The map definitely shows people (humans) inside the castle, but I remember reading about Harry watching Peeves bouncing around in the trophy room and Peeves is not human. I don't remember if I had exactly read it or not, but the wiki page for the map says that it shows the ghosts as well.
What kind or creatures or beings come under the map's radar? Any living creature? Or humanoids? Or creatures with a significant size or intelligence? Would it show the house elves in the kitchen, centaurs in the forests and the merpeople in the lake as well? What about the giant squid and the thestrals or unicorns? Would it have shown the troll from the Philosopher's stone if they had the map then? What about Quirrell/Voldemort? Would he have shown up on the map? And the basilisk from the Chamber of Secrets (the book)? Maybe the chamber itself was unplottable but if the map could show the basilisk he would have been visible when he was slithering around in the pipes.