Although cats have a reputation for being solitary animals, they have developed an elaborate system for communicating with each other. Scent, body language, touch, and sound help one cat learn about another. Your cat will use the same tools to communicate with you.
Following Their Noses
Odors are one of the most important ways your cat learns about his environment and other cats that live in it. If your cat lived outside, he would use urine to scent-mark his territory, backing up to an object, squirting urine on it, and leaving a pungent odor for any feline passers-by to smell. While not having the effect of keeping other cats away, urine marks alert other cats to the presence of the marking cat.
If you've had your cat neutered before he began spraying, he should not urine mark inside your home, but he may use his sense of smell in other ways to identify his space.