As a rule of thumb, always have one more litter box than there are cats in the household. They should not be in the direct vicinity of the feeding place. Unlike dogs, cats are housebroken very early - from the fifth/sixth week of life. Like many other things, this is already taught by the mother.

Find the optimal size
The most important factor when choosing a litter box is size. Your cat should have enough space! She needs to be able to turn and stretch comfortably and needs enough space to scratch. It is better to buy a toilet that is a bit too big than one that is too small.

Advantages of a closed litter box
There isn't as much litter going around when the cat scratches, and the smell doesn't spread around the home as easily. Cats don't feel like they're being watched and can go about their business in peace.

So that the cat litter stays in the litter box
The higher the edge of the litter box, the less risk there is of your kitty scattering the litter all over the apartment when scratching.