Cats have specific resource needs for their environment. They are basic needs and can be simple or advanced, as long as they are appropriate for the cat.
Fresh food and water, litter boxes, scratching, climbing and hunting opportunities, relaxation and comfort are some of the primary needs of cats. It's not only important that they have these resources, but that they are readily and safely available. The more cats are within an environment, the more resources will be necessary. Cats will share, but they would rather not. If there is only one resource for multiple cats, there is a risk of guarding and ambushing at that location. This is true regarding food, water, cat trees and even litter boxes. Multiple resources will facilitate harmony among cats.
Resource Placement
Easy access to resources will ensure they are used as well. Along with easy access goes comfort with the area. While deliberating the location of resources such as cat trees, for example, realize the vertical nature elevates cats out of activity at ground level. Because cats often enjoy solitary time, it doesn't mean they are rejecting family. Cats are part of the family and do enjoy "hanging out." Offering cat furniture in family areas is an excellent way to accommodate these needs. The same holds true with cat scratchers. There should be many in the home, in family and sleeping areas at least. Think of the appearance of a well used look of a scratcher as a badge of honor for yourself. Your kitty prefers this magnificent resource as opposed to the hardwood or furniture in the home! So display it, don't hide it. If hidden, kitty may not frequent the area to use it.
Hunting Opportunities
Relaxation
Providing the required resources, and in sufficient number and locations, leads to an enriched environment. An enriched environment alleviates boredom, fear and loneliness, etc.. When kitty lives in a balanced mental and physical state, there is less opportunity for unwanted (by humans) behavior to arise. Equilibrium can be achieved with careful consideration of kitty's needs and placement of resources within the home.