This is interesting, but I worry the premise is a little too flawed from the start and may need some adjusting.
For starters, the industry is not that evenly distributed. Rather than cities that are "better known" for game development than others, you actually mainly have "cities where there are studios" and "everywhere else," at least as far as anything recognizable as a studio goes. As Kylotan says, a large majority of indie "studios" aren't operations like you're probably expecting. They're just folks in their apartments, garages, basements, whatever.
Second, it's unclear what you mean by "steering the medium." Games are not a monolithic thing, and while indie studios and loners making games far outnumber the larger, "AAA" type of studios, they do not generally have enough combined influence to really "steer" anything in a noticeable fashion. The games industry is not a winding river, it's a bunch of tiny little rivulets each forging off in their own direction, with almost no concern or regard for what the others are doing. Those are your indies; they're doing they own thing, but they're not effecting global changes for the most part.
Third, game studios aren't like retail shops, and many of them will be uninterested in talking to somebody who from their perspective is just a random fan. I would caution that a better way to plan your route is to instead find a list of every studio you can, call them, present your credentials and explain your plan, and see if they'd agree to a face-to-face meeting. Then plan your route around that, so you know somebody will actually be willing to talk to you when you get there.
Fourth, "cutting edge" can mean a lot of things. It can mean pushing new technology, pushing new gameplay, or pushing totally new ideas about what a game should be. Usually any particular developer might be trying to do one of these (or good at one of these), but rarely more than that.
Finally, a lot of the collaboration your thinking of -- probably the majority of it -- between the indie-as-in-from-home developers happens online. It's not a field where there is an absolute requirement to be physically co-located.
I'd suspect you're going to end up in the major cities of the regions, the Londons and San Franciscos of the respective countries (I'm not as familiar with the geographical makeup of the industry outside the US so I'm not going to be too helpful in suggestion which cities, specifically), as that's where things tend to cluster... but I'm not quite sure what you will find there in reality is quite what you are expecting.