When all sides of a pool or spa are vanishing edge, you have what is known as a perimeter overflow, (also sometimes referred to as a wet edge or wet deck.) In this case, there are no visible edges to the pool or spa. Water flows over the edges on all sides, into a hidden catch basin. The edge may be elevated to spill into a catch basin below, or it might be flush with the edge of the deck, which means the overflow will spill into a narrow, hidden catch basin underneath the deck.
A stunning visual effect, this is the most difficult of all vanishing-edge designs, and should not be entrusted to anyone but experienced professionals who specialize in vanishing edge and/or perimeter overflow design and construction.