When exploring Twinity Singapore for the first time, I wandered far enough from the city center to get to the point where the city, quite literally, stopped. Metaversum hadn't gotten around to building those remote parts of Singapore. I was looking at the seams of the city, so to speak! Today the same happened, but this time in London.
Somewhere between Picadilly Circus and Knightsbridge, near Green Park, the city ends abruptly. I was on my way to Hyde Park and Kensington, but it seems those areas haven't been built yet.
By the way, as I Tweeted before: from my admittedly anecdotal evidence, I'd say Twinity London is busier than Singapore, and perhaps Berlin as well.
More snapshots at my Koinup page.