Stellar Cartography used to show habitable planets as yellow dots on the mini-map so you could more easily find planets during the colony rush, instead of having to guess or explore every star. Now, stellar cartography is absolutely worthless to even research, ever, since it helps in no way at all (unless the number of planets is set to a very very low number). The only thing it does do is bad, which is cluttering up the mini-map with tons of extra grey dots everywhere unless you are zoomed out quite a bit.