Cats are tame animals, and they don't usually let people touch them easily. However, when a cat trusts you, it will allow you to touch certain areas, which are usually areas that they rarely clean themselves or are quite sensitive, such as the head, abdomen, and back. 
First, a cat's head is one of its most sensitive areas, and it usually only lets itself or someone it trusts very much touch it. If your cat frequently lets you touch its head, it means it trusts you a lot.
Secondly, a cat's abdomen is one of its more sensitive areas because it is very delicate and easily injured. If your cat frequently lets you touch its abdomen, it means it trusts you a lot and that you have a very close relationship.
In addition, a cat's back is one of the parts of its body it is more willing to let people touch, because it is difficult for them to reach that area on their own. If your cat often lets you touch its chest or back, it means that it trusts you a lot and is very willing to be close to you.
