McLoud is the author of Understanding comics, one of the best book about comics I've ever read.
In this book, McLoud introduced a map of visual iconography that took the shape of a triangle.
The lower left corner was visual resemblance (e.g., photography and realistic painting). The lower right included the products of what he called iconic abstraction (e.g., cartooning). And at the top were the denizens of the picture plane ("pure" abstraction) which ceased to make reference to any visual phenomena other than themselves. The move from realism to cartoons along the bottom edge was a move away from resemblance that still retained "meaning," so words, the next logical step in the progression, were included at far right, thereby enclosing anything in comics' visual vocabulary between the three points.
See also: http://www.scottmccloud.com/inventions/triangle/triangle.html