What kind of drawing format is this? Pictures with litle box on top left

Question

Sometimes I find art like these on Pixiv

Sources:

• https://www.pixiv.net/member_illust.php?mode=medium&illust_id=29538975
• https://www.pixiv.net/member_illust.php?mode=medium&illust_id=51254835
• https://www.pixiv.net/member_illust.php?mode=medium&illust_id=60499300
• https://www.pixiv.net/member_illust.php?mode=medium&illust_id=63393567

The little box on the top left is usually blank and something is written in the square box next to it - sometimes it's the artist name and sometimes it's not. And usually the picture's title starts with 'C' and is followed by a two-digit number, although not always (see links).

What kind of drawing format is this? What's the little box on the top left for? And what's the meaning of 'C..' in the title? And what does the number stand for? Sometimes the title starts with 'C..' but doesn't have the same format, like this.

Note that two of the five links I provided are from pro artists. They are Akio Watanabe, the character designer from the Monogatari Series anime and Shinobu Shinotsuki, the illustrator of the Youjo Senki light novel.

Answer 1

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:

1. A little box on the upper-left: Indexing/Stall location (to be explained later)
2. Text inside the box on the upper-right (or none): Circle's name
3. The rest of the area: Free image, can be a unique image for identifying the artist, or anything related to the circle's current merchandise

What's the little box on top left for?

The little box on the top-left is used for Indexing/Stall location. Inside the catalog, there's a list of circle-cuts with their stall location, as shown for example in the Comiket 90 catalog:

^{Catalog for Comiket 90, date 12 (Friday), East Hall 4-6. Left page showing stall モ43-モ60, right page showing stall ヤ1-ヤ17}

For reference, this is the map of Tokyo Big Sight for East Hall 4-6:

^{Map of Tokyo Big Sight, East Hall 4-6}

And what's the meaning of 'C..' on title? And what does the number stand for?

It's the identification of the n-th Comiket.

As mentioned before, it's used in a doujinshi market like Comiket. Comiket is done 2 times per year (summer & winter) and each event is always identified by its serialization/number, such as Comiket 92 (C92) in this Summer 2017.

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Reference:

• What the heck is a "Circle Cut"?!
• Comiket Event Report Part 2 - Guidelines for Comiket