What is the projection used to display ”the Universe” maps? What is the left edge, the right edge, etc. They seem to be similar in all articles but I have no idea how map relates to e.g. a night sky?
The illustration in the article ([1]) seems to be a (slightly cropped) Mollweide projection [2], in familiar equatorial coordinates such that the north pole is top center, south pole is bottom center, and the equator is a (imaginary) horizontal line in the middle. The region of acquired dark matter data is located in the southern hemisphere sky, which makes sense given that the observatories used were in Chile. At the bottom you can see the Magellanic Clouds, satellite galaxies of the Milky Way which can only ever be seen from the southern hemisphere.
From what I can tell, it's a projection of a view from the night sky from one particular telescope on Earth. They sampled a bunch of galaxies in an area about one eighth of the night sky.
The background starfield appears, in fact, to be a projection of the entire celestial sphere, all 360°×180° of it, so only a half of it at most can be seen at a time from any point on Earth.
