You are correct: Comiket is the world's largest convention for selling/buying doujinshi, and includes cosplayers. However, it is not an anime/manga convention and as an experience is pretty much nothing like Comic Con or similar conventions to Comic Con such as Anime Expo.
Yes, Comiket only exists in Japan, as over 550,000 Japanese doujinshika (a.k.a. ...
What kind of drawing format is this?
It's a "Circle Cut".
In this context, "Circle" means "Doujinshi circle", and "Cut" means "Cut-out". It's exclusively used in a doujinshi market place such as Comiket, Comitia, etc to be used in the catalog.
The format is:
A little box on the upper-left: Indexing/Stall location (to be explained later)
Text inside the ...
Both Comiket and COMITIA are doujinshi conventions held in Japan. Both conventions are generally the same event with several differences. See What events usually happen at Comiket?
While both Comiket's and COMITIA's main focus is socializing and exchange doujinshi. COMITIA is the largest dojinshi convention focused completely for the exchange of ...
There is a small amount of officially-released statistical data in English here.
The "History of Comic Market" section of the "What is Comic Market" PDF shows a chronology chart of the number of participating circles (32 in the first Comiket, up to 550,000 in a recent Comiket), and the following pages of the PDF list more specifics.
In terms of volumes of ...