Cats can use their urine to say "back off" to other cats. They tend to do it when they're in conflict with another cat, feeling insecure, or looking for a mate. If there’s conflict, many cats in the house, or changes in routine, there’s more chance a cat will mark their territory. To stop the spraying, have your cat neutered or spayed. Use an enzymatic cleaner where they have sprayed. If your cat keeps spraying, ask your vet for advice.