I've just finished judging the entries for the seventeen-year-olds in the Power of the Pen contest run by the public library. The choice this year was more challenging than last; for the first time I gave out several Honourable Mentions, something I had never needed to do before. There were five poems vying for two places. I gave the three that didn't win or place those honourable mentions.
The entries became a goad to write about shape in poetry, as it differs from form. Most of the entries were centered rather than left margin justified as is the usual manner. Centering, especially three or four word sentences for no specific effect, becomes very annoying. Almost as bad is the "concrete" poem. We all know them: the love poem shaped like a heart, the angel poem shaped like wings, the one about trees taking the form of a tree.
But sometimes a poem takes on a shape of its own, something internal that is part of its manner of expression. It may indent different lines from the margin for emphasis of those lines. Different margins for differing length of line may be used. The first word of a line may be placed in relationship to a word or phrase in the previous line, stressing how it expands or defines that word or phrase. The reasons go on.
Here is an example of its use by e. e. cummings.