A piece of paper with two directional black lines drawn on it crossing each other, forming four quadrants.
https://files.mastodon.social/media_attachments/files/116/773/380/876/743/032/original/b6d07290ae49d5ac.jpg
Pull out a piece of paper and draw two lines on it. You're doing something you've seen a million times since grade school (it's a useful way to think about multivariate space!), using two different directions to divide the world into quadrants.
Like this:
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