These are very fair questions about map and combat readability that can be a bit complex due to the different types of vision/zoom in game. I'm not a VIP and haven't played since Lucy Opendev, but I'll give it a go based on the recent Unity Showcase. 

Cities can generally be distinguished from outposts by names, production cue, and quarter count around them. Outposts in the Unity showcase usually carry the culture's name but some in the showcase were seen to have particular names. None-the-less, a large "detach/attach" button below outposts will make then easily identifiable. View level is important here as the more zoomed out a player is the more general & empire wide view they have. 

Administration centers for attached territory are easy to identify if you own them as players can see resource yields in the management screen. Identifying another culture's admin center in an attached territory can be done a couple of ways. Usually targeting the most grandiose structure does the trick but hovering over each quarter for the tool-tip would provide a more exact answer. 

Units are a different issue as on the world map multiple units can stack together to form an army/fleet. It would be very difficult to have individual icons distinguishing each type of unit within a stack. To my knowledge, different types of units don't have unique distinguishing icons as their base trait determines its abilities & icon in battle. For example, a musketeer is an infantry gunner yet a Russian Cossack is also a gunner but mounted. Both units would have the same distinguishing icon as they have the same base "gunner" trait yet these units have different stats. It would be a hefty task to design icons for each unit within the game before release... 

In combat, units can be distinguished by their distinctive model and portraits at the center of the screen when ordering units around. Sure, some units may share the same icon above their head but that can be used to narrow down the possibilities. There are only so many generic and unique units per era; so with some experience players could possibly tell each apart from appearance alone.

Would it be nice to see units with unique distinguishing icons... Sure... but that can only ever go so far especially if every unit on the field is the same unit. At that point, would players want/need a Hp bar above each unit's head to distinguish a particular unit apart from the cresh?