Life In 19x19

While doing some work on the professional title pages on Sensei's, it occurred to me that I never heard an explanation of these two terms that are used.

Now, the big titles have more or less the biggest prizes in Japanese Go. Is that all there is to the classification, or does it have some greater significance? Note that the Agon-Kiriyama Cup has a larger purse than the Gosei, and is or was played with 2 hours thinking time in many rounds (though 1.5 in the finals). That's quickish for professionals, but not what we usually think of as blitz.

Even less clear is how "official tournament" is used. You see it on pages like Cho Chikun's, where the Yugen cup is described as unofficial, as is the Daiwa Grand Champion Cup. One obvious question is "official for whom?" given that there are two Japanese professional organizations.

Lastly, does the concept of "Big Title" apply clearly to China, Korea and Taiwan? The professional tournaments page lists 3 tournaments for each of China and Korea, but I have no idea what that's based on or whether the lists are complete.

On http://senseis.xmp.net/?NihonKiInNewPromotionSystem it says certain tournaments guarantee certain promotions. Maybe that has something to do with it? Don't know about Korea & China.

That is, as far as I can tell, a third division there. Some of the titles that count for promotion are not typically classified as the "big" titles (Agon, Ryusei, Shinjin O), while the NHK is official, so far as I know. The same is true of the female tournaments.