HEALPix (en.wikipedia.org)

Love the HEALPix scheme, super useful for indexing too (some similar characteristics to geohashes).

I used healpy[1] once during my undergraduate years. It was a summer project to develop an algorithm to find void galaxies.

[1]: https://healpy.readthedocs.io/en/latest/

I recall when I first saw Ubers’s H3[1], it really reminded me of healpix (from grad school). I know the algorithm is different but similar problem space: “given a point on a sphere, assign it to a stable cell ID”

1. https://www.uber.com/us/en/blog/h3/

See also HiPS maps, which map the sky onto ever finer HEALPix grids to allow zooming: https://aladin.cds.unistra.fr/hips/

Also very cool: Google's S2 geometry - https://s2geometry.io/

Used by https://catch.astro.umd.edu/