Unowned cats often live together in groups called colonies. They develop a social structure and have strong bonds between the colony members. Some are strays who once had a home, but many are born in the wild and fear humans.
Traditional animal control considered cat colonies a problem, and attempted to solve it through removing and euthanizing the cats. That method creates a "vacuum effect" where cats just move in from surrounding areas.
TNVR - Trap, Neuter, Vaccinate, Return - is a more efficient and humane approach. The cats are trapped in humane traps, examined by a veterinarian, spayed or neutered, vaccinated, and identified by an ear tip. If you see a cat that's missing the very tip of an ear it means it was a part of a TNVR project and has been spayed or neutered.
Cats are returned to their colony and managed by a colony caretaker who ensures they cats have food and monitors the ongoing needs of the cats.
If you perceive community cats as a problem, download the brochure "Living with Cats in your Neighborhood" - it explains TNVR and gives suggestions on how to solve common problems.