There are also routing rules. An airline might divide Asia into two or more parts, and it may cost more to connect in one part of Asia if you're end destination is in a different part of Asia.

Another kind of routing rule is direction of travel: AA, for example, considers US<->India awards to be trans-Atlantic only. If you want to fly trans-Pacific (say, because you're starting from the USA west coast), it has to be booked as two separate awards (which doesn't cost double, but does cost more).