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I'm a huge fan of alternative Tube maps. And the one above may just be the most ambitious I've ever seen. Using TFL's current London Underground map design, F. Dans has added in most ghost stations, unbuilt lines and disused extensions.
There are many interesting features, such as the District line out to Windsor (which did exist for a short time), the readdition of Aldwych and other Ghost stations and the addiiton of the proposed (but never fully built) Northern Heights extension.
However the one thing that really stands out to me, is that even with the addition of many proposed lines, few would serve South London. It remains a Tube wasteland, although one that is very well connected by rail (not seen on the map).