Spacing is a no-brainer, they have restraining orders built into their DNA. The real question is why face the same direction? They perhaps all bought their GPS from the same defunct company.

Perhaps they belong to a platoon of some sort and they're in formation as well as nature's uniform - and they're all standing "at ease"

 they could also be a highly trained militia group and have a platoon sargent - "left face - right face," etc.  -  maybe even trained to eleminate with extreme prejudice - LOL

Then again, the black, gray white  color scheme is an indication of formal attire - maybe they're escorts for contestants of the  Ms. Aviary of the Universe contest? 

 No, I would say clearly a black tie affair - they look too cool, calm and collected.  Almost as if they're waiting for the curtain to rise and the music to begin. 

  Have you noticed their lofty manuevers and formations over the Cuyahoga River during NEO winters?! 

Definitely, a more highly evolved species for their capacity to live together--Humans call them Ring-billed Gulls...

Warming themselves in November sunlight on the south side of Ontario Stone gravel piles at the mouth of the Cuyahoga - with a slight SW wind coming from the left of the image - probably explains their location on the piles and their orientation primarilly facing to the left of this image. 

The spacing is not as clear: does the distance between them just keep being reduced as more alight? Or is the distance between birds the necessary wing spread needed for take off?  

On the water these birds seem to prefer being further apart - (longer take off distance required in water) or is there just more water area than gravel area?

On warfs and docks these Ring Bills are quite close together - as in this grave pile image.

But in each example the distance between them seems to have a clear norm across the entire flock (is flock the right word here?).

Do humans do this too?

Again, maybe a flight formation pattern for a quick and hasty lift off - or could be just simple respect for giving each other "breathing room." Either way or for what ever reason, gives the human mind something to think about and also let's you know that these little birds are thinkin' beyond the moment. 

I like 'em and think they are beautiful.   "Birds of a feather flock together."