Well, don't keep us in suspense! Share! 
It is, quite simply, the degrees of tilt of the planet north and south of the equator. For instance: Earth's axial tilt is 23.4 degrees, and the Tropics of Cancer and Capricorn are 23.4 degrees north and south of the equator.
Oh, I thought you were going to tell us how to compensate for water dispersal on other axial tilts. 
I'll have to research it on my own.
I'll have to research it on my own.That is a tad beyond my abilities, I'm afraid.