  Islands are combinatorial objects that can be intuitively defined on a board
consisting of a finite number of cells. Based on the neighbor relation of the
cells, it is a fundamental property that two islands are either containing or
disjoint. Recently, numerous extremal questions have been answered using
different methods. We show elementary techniques unifying these approaches. Our
building parts are based on rooted binary trees and discrete geometry.
  Among other things, we show the maximum cardinality of islands on a toroidal
board and in a hypercube. We also strengthen a previous result by rarefying the
neighborhood relation.
