Now, that's irritating. Me, I mean. When I gen these tantalizing shapes all pixelly, I start to care about every pixel. Which eats a doofus quantity of time twiddling bits. Siiiigh. So, fairly well cleaned up, here's the overall view.

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One OTHER thing irritating about me, to me, is that I'm kinda dense about learning lessons. Can't tell you how many times I've 'found edges' to make a coast, and realized steps later I intended to define edges onshore instead of out to sea. The result of that here is basically the first one to three pixels of shallow water is all black. Hmph - musta been a wicked oil spill. BUT I had already generated depth curves - call 'em 2.5 fathom and 7 fathom. Trouble is, most of the zero to 2.5 fathom band is hidden by that oil slick. I had intended that zone to be inconvenient areas too shallow to anchor big ships, leaving that to the 2.5 to 7 fathom band. "Big" being frigates and modest ships of the line - call my equivalent date early 1800's.

So now maybe I'll gen a 2.5 fathom line a bit farther offshore. See that circled area? That's the inner harbor - probably needs some dredging too. Aaaand I will exercise my Rationality License and fill in a bunch of the deeper pockets in each of those depth bands - after all, real silt would do just that.

Like mechanically fractal terrain, this cloud generated rather too many lakes -- I deleted many. Also like many Landforms Of Randomness the surface would be inconveniently rough, and not pleasantly plausible, so I'm going to take the tack most harbor charts do, and ignore the landforms. Except those reasonably expected to be markers for navigation, of course.

Scale of the oval is something around 10-15 miles across.