stellaris
I've just started a new game, and am exploring the various options. I've run into the planetary details screen. Each tile can support one building, and one population. Thing is, I noticed these little + arrows next to some buildings, and hovering over them gives me adjacency bonuses.
What causes this? Is it specific buildings that improve the spaces around them? Is there a list of adjacency combos?
Nope. Doesn't look like it. Hand-drawn circles for your pleasure.
So first you need to recruit the army on your planets. Then if you select that planet and go to the armies screen, in the top left of that panel there is a button named "embark all" this will move all your armies to the orbit of the planet where you can then move them like regular ships. Now move them to an enemy planet and you can click the button to land all of your armies. It's advised that you first bomb the planet to destroy fortifications and increase the chance your armies will be able to take over the planet.
Best Answer
As far as I'm aware, the only buildings with adjacency bonuses are the Planetary Capital line of buildings (and their upgrades) starting from the Planetary Administration (after upgrading the Reassembled Ship Shelter).
In this case, as per their descriptions, they provide +1/+2/+3 to production of adjacent Minerals, Energy, and Food. Sorry, scientists!
These 3 are listed on the Stellaris Wiki, and there don't appear to be any others.