San Francisco: coast, deep water, and a broad sampling window
Water-class cells account for 25.8% of this sample; 18.2% remain automatic. Those two shares explain why the preview is more informative than a single “coastal” tag: it shows both classified water and areas the source did not settle.
The report minimum is about −3,644 meters. That low value comes from the sampled elevation field, which includes offshore terrain; it is not the elevation of the city’s streets. The heightmap download also uses per-sample land normalization, not a globally shared grayscale height scale.
Before starting a build, inspect the preview and then use the game link to see the actual available terrain. A data-derived coastline is not a map of today’s roads, bridges, or parcels.