Outdoor hazards are
obvious such as: volume of traffic, incidence of disease, a cat's ability to protect itself (deaf, partially sighted, frail), its
danger to other cats (if it has a transmissible disease), predation upon vulnerable wildlife, any
danger to humans (a British cat, Gizmo the postman hater, had to be confined for the safety of postmen and other delivery
men),
danger from humans (e.g. gamekeepers), spilt car antifreeze and garden chemicals.