Alan s,
While I appreciate you taking the time to reply to this thread, I'm not sure you're understanding what I am saying here.
I'm not sure if you've ever been to places like Berlin, Melbourne, Vancouver, or Calgary, but developing a sense of direction means very little when you don't know the city. Especially in places like Berlin where it is wall to wall buildings that were built in the GDR era and look almost identical throughout half of the city.
Just to help you try and visualize this. Here is the map of the Berlin Wall Trail that I rode.
Mauerwegcomplete.jpg Photo by Auntie_Helen | Photobucket
This trail follows the historic route of where the Berlin Wall used to be. To ride it, allows you to get a sense of what that city was like before the wall fell and to experience many interesting historical landmarks. There are many parts of the trail that are well marked, but others are just simply not. There are parts of that trail that weave through little neighbourhoods, forests, highways, and even requires taking a ferry at one point.
There is no way, that "developing a sense of direction, from the surroundings" would be even remotely possible here. I know this because before I mounted my external battery I rode 65KM or so, and found myself with a dead phone unable to find my way back. I had to use my very limited German to find and S-Bahn that would take me back home (even then it took me hours due to getting on many wrong trains).
I'm sorry, but saying that I should "develop a sense of direction" is not only ignorant of reality, but a tad insulting as well. As a matter of fact, I actually enjoy my rides even more because I don't have to worry about riding off into an unknown city and finding myself lost, or worse, in an dangerous area. Having a bike mounted phone allows me to enjoy the sights, instead of worrying what direction I'm going.
However, if you're still not convinced, here is a challenge.
Bring up Google Maps and type in any major city. Now, pick your starting point (which will be your ending point as well). Now, go to street view, and navigate your way through say, 30KM of the city. Try and find your way back home without looking at any other means of navigation. I am curious how well you would do with your heightened sense of direction. If you get back to the same place you started, without finding yourself in any dangerous situations, or getting lost (or taking 8 hours)...then you will have my upmost respect.