how Create an isle surrounded by sea

Hi all, i need to create a map with an isle surrounded by the sea how to do that? i have create a simple terrain landscape now how can i make it circle and with sea?c9008c3763819129579569cf70924db092fcbf93.jpeg

Use the Landscape tools to create some definition to your current landscape plane. Then create another plane and set the Z axis the same as your current plane. then assign a water material to the new plane.
There are other ways to do this, but this should get you started.

I have always wondered, is there some special shape for a plane? Like just a plain square that I can use for my oceans?

Every plane could do the job. Sometimes it is nice, to have them with more vertices, but for a flat ocean with dp-mat a single face is enough, if you ask me.
Should i “model” one for you?