Anime’s aspect ratios

Anime-Gataris (2017; before you rush to try this: it doesn’t manage this kind of wit often)

Aspect ratios go unremarked, but few things can be more fundamental to an anime than its shape. To my knowledge, few things have been said on the topic. Jamal, voice of the podcast Get in the Mecha, has covered it a little, in an episode which helpfully reminds us that aspect ratio is a choice. Jamal’s treatment focuses on aspect ratios’ artistic ramifications, though, so I thought I’d have a go at gathering some more basic historical information about them.