Where do the water depths come from?

From the worldwide sea floor model the elevation tiles carry. The builder reads it round your island and places each step so it covers a fair share of the water you can see, at depths a chart would print. Type your own depths under Look if you prefer. The sea floor model is coarse far from shore (about a mile per reading), so each step is also kept at least a little wider than the one above it, and every sheet always shows.