Cat Behaviour and Training – Enrichment for Indoor Cats

There are many circumstances in which keeping a cat indoors may be safer for the cat and therefore, arguably, better for the cat. Indoor cats are at lower risk for injuries associated with the outdoor environment (e.g., cars, trains, dogs, predators, humans) and are at far less risk of contracting parasites and infectious diseases such as feline leukemia, feline infectious peritonitis and feline immunodeficiency virus.
Studies have consistently shown that urban cats that go outdoors have far shorter life spans (averaging 2 years or less), while most indoor cats will live over 15 years. Keeping cats indoors also prevents killing of wildlife, fouling of neighbourhood yards, and fighting with other cats. Depending on your cat’s personality, it may be safer for other cats and wildlife in the neighbourhood if you keep your cat indoors.If you decide to keep your cat as an indoor pet, you will need to be very aware of the extra responsibility that an indoor cat brings. You must take the time and trouble to ensure that the indoor environment offers the cat the opportunity to express as many of its natural behaviours as possible.

for more info What do I need to do to make my indoor cat happy?