How it works
Athelstan Spilhaus wanted a map with the oceans as one body of water. He took Oscar Adams'
1929 conformal map of the whole sphere in a square, and turned the sphere so that the square's
centre sits in the Southern Ocean and its four corners fall on land.
No light, cone or cylinder makes this map: Adams built it from elliptic integrals. So the
surface here is the map itself. A grid over the square is carried back onto the sphere, and
Unfold moves every point in a straight line from its place on the globe to its place in the
square.
The orange lines are the square's own grid. On the globe they still cross at right angles,
because the map is conformal, everywhere but the red corners. There the full turn around a
point on the globe is squeezed into the square's corners: one corner each in China and in
Argentina, while the other two corners are the same point in North America. The square's
edges fold in half to close the globe up again.
Move the centre or the azimuth for your own oblique Adams square. The projection is a port
of PROJ's spilhaus and adams_ws2 (Evenden, Evers, Wilkinson and
Jimenez Shaw), checked against PROJ.