The East Island of Black Water/Eaux Noires

An extensively-detailed topographical map for the prosperous eastern island of Black-water, a province in the archipelago nation of Carcosa.
Very little geographical information existed about this island prior to my cartographic work, other than a geo-political outline from the virtual game and a vague role-play concept of scale (the large city in the north, also called Black-Water, is described as being equivalent to ancient Alexandria or Constantinople in size and prosperity). The same city has been described as covering most of the island, however, since the largest of the three Carcosan islands was compared to Switzerland in size, such a population spread would be impossible even with 21st century levels of urban sprawl.
The game is set in a pre-industrial world, so the concept of a single city covering an entire island of that size is vastly exaggerated.

Another reference for scale: the distance between this and the neighbouring west island has been described as "reachable by a bridge" however there have been bridges constructed in our world that span more than 30 miles, so this definition is also relative. Looking at the placement of the islands against the greater world map (and assuming 1:1 consistency with the depiction of the rest of the map) also helps determine distance, since it takes many months for a ship to sail around only 1/3 of the entire game world.

My final scale has the islands set 6 miles/10 km apart.
The shortest part of the English channel between England and France 33.3 kilometres (20.7 miles; 18.0 nautical miles).

To deduce the correct scale for topography, I looked up real-world islands in terms of size and sketched the shape of mountains to as closely as possible resemble the geopolitical map. To explain the name of Blackwater (as well as the curious shape to many of the outlines) I have made the region volcanic, which also contributed to place names such as Obsidian Strait and Black Glass Garden, as well as the presence of hot springs.
I used islands such as Bali, Buru and Corsica as my main geological references, since their sizes are comparable to that which I've determined for Blackwater (Buru being the closest).
It took two days of research to deduce what scale the map should be drawn to, since I was aiming to create a hyper-realistic topographical map, rather than an exaggerated map... though this would have been *much* easier.
I needed to rework my original sketch after discovering the existence of other maps that I hadn't previously seen in my research, however they were also drafted after the same geopolitical reference I was using, some even contained mistakes.
I overlaid all of the maps together to determine an outline that would agree with all of them, but the geopolitical reference took dominance. I used the lines that divide the island into domains to dictate the placement of a volcano, as well as several ruins and a river gorge. I also ended up using a lot of the "noise" in some of the maps as reference for a second map, which shows underground passages and waterways flowing beneath the island.
For role-play reasons, the full version of this second map remains confidential, but there is a sample included above.
I have used no key for the map, since I hope that it is self-explanatory, but there is an indicator of polar north as well as two scalebars.
Cities and towns are labeled with larger font, places of interest in smaller font. There are paths in the water showing shipping routes, which also indicate major ports.
The 8 pointed star showing the cardinal directions is also the sigil of my ship (the Morningstar) in the game.
I expect the location names will be revised once Francophone speakers and other players of the game have given feedback on the map, but for now these are placeholders for role-play and exploration.