In real life, the African continental plate is being subducted under the Eurasian plate, and being melted into magma. In Failbetter’s universe, it’s still being subducted, but instead of turning into magma, it’s emerging in the Neath. The African continental plate’s upper right end matches the Elder Continent pretty well, too. Of course, the Elder Continent extends farther east than the African plate. That’s where the Arabian plate comes in. It was once part of the African plate, only 25 million years ago, and the hypothesized location of the Garden of Eden. I have no clue what the Western Continent is, though. But, since, for some reason, Fallen London is underneath its original location on the surface, since you can escape with your spouse to a village in Somerset. Here’s the link. http://fallenlondon.storynexus.com/Profile/Jamieson%20Well
That leads me to believe that the Neath is actually tilted a bit, or the Sunless Sea map is less accurate in the placement of the Western Continent’s shores.