I've looked all over for a simple mod that would suit my needs, but as I can't find any, I'd post it as an idea.
I often find myself confused as tho exactly where I have claimed an area. Righ now, me and my friends are working together, and we all induvidually claim all over and trust each other so we all can access everything we build. Sometimes there are gaps of unclaimed areas and to solve this, we need to claim areas in squares that goes well with other squares, not making someone shorter or longer. The current solution is to run around with a stick and right-click like a mental, but it's still hard to mentally visualize the claimed areas.
I think it would be very nice, if not extremely userfriendly (for newer or younger player) to be able to visually see every claimed area nearby with a push of a button. Having 3 different colors for My claimed areas, trust friend claimed areas, and other player claimed areas. This would greatly improve the efficiency of claiming and the gameplay in general.
I don't know if the information about the claims would be accessable from a client side mod, but that's at least what I would prefer, avoiding the need to make the hosts update their servers.
Another, more finicky solution, would be to manually plot in the coordinates of your claimed areas (which you usually can access through a command) and then either show it as an overlay on the blocks in the minecraft world itself, or in a map/minimap.