Community Lot Issue

Got it, thank you.

Yes, thats correct: The gray icon is a community lot, the purple one is a home lot.

The name “Community Lot”  has nothing to do with the lot sizes. It means, your Sims can’t live there and when building and decorating houses on those lots, you can use certain items for free.  

Both lots in your screenshot are Extra Large with the size of 54 x 36 squares. You can only build houses there, that fit in 54 x 36 squares.

The Duketon University has 18 x 36 squares, so it doesn’t fit in 54 x 36 squares. You can build it on any “Ocean View Residence” in your town. It doesn’t have to be built on a Community Lot. If you want to build it on one, you can only use the Barter Boardwalk lot.

From what I understood all the lots with the picture on the left circle were community lots and the purple circle ones were x-large ones. I have tried looking it up but couldn’t find anything saying otherwise. Why would it be marked differently? 

The lots shown in your screenshots are Extra Large lots, but the Duketon University only fits in an Ocean View Residence. That are the lots by the ocean near the bridge to Mysterious Island and the light house, the lots on Mystery Island and Barter Boardwalk in Sim Springs.

It’s confusing that Barter Boardwalk is shown as Standard Residence, but in fact it has the same size like the  Ocean View Residences.