Watch it generate. Hold space to pause until space released. (Recommend using this with any other tools) Hold E to erase tiles. I like cutting islands in half and watching the islands try to re-assemble
Btw this appears to be the same as "terrain generate test 1" but the generation code was near completely re-written. I got the idea from how wave function collapse works. It's not exactly wave function collapse but its a bit similar. Pretty much, at the start forest tiles are randomly placed on the map. Then it uses these rules: Forest tiles can only generate grass, forest and nothing. Grass tiles can only generate sand. Sand can only generate sand. Water can only generate water.