I have a space of concrete on one side of my pool that is basically 4 feet wide by 30 something feet long. I've devised a kata practice set that works perfectly in this space. It's the three Naihanchi kata, followed by Rohai, Passai, Chinto and Kusanku. It's a perfect advanced kata workout and it fits the area perfectly.
If you think creatively, you can always find a place to train.