Straight lines laid along the edges of the squares.
Straight, bent or tilted?
Checkerboard bulge
Is this checkerboard flat, or does its middle swell out like a ball?
It’s flat: every line between the squares is straight.
Why? Each little square in a corner makes the edge beside it look slightly tilted, like the café wall’s tiles. Around the middle they tilt every edge outward, so the board seems to bulge. Akiyoshi Kitaoka made many like it; this is our drawing.
Picture: Drawn by Science Playground, after Akiyoshi Kitaoka