Tom of A Common Reader is very enthusiastic about Google Earth for intensive book-reading purposes. My lily-livered computer can't deal with it, but there is a "Google Book Layer" available on your bog-standard Google Maps. You can look at maps of the world with pop-ups of book extracts mentioning the places on your screen. I have to admit though, it doesn't get my tail wagging. Too slow at my end and not much to show for it, as few of the English-language books in the system mention German locations. And although there's a distinct purple blob above Berlin, I can't actually click on it.
But never fear, for those enterprising Germans have got the GPS-books thing all sussed out for themselves. I'll tell you all about it in a moment, but first a minor digression.
I'm a closet (well, not so closet now) William Gibson fan but I was a bit nonplussed by Spook Country. That may have been because I didn't understand the technology in question, actually, in contrast to Pattern Recognition. But there was this tumblr thing called node that provided kind of bizarre cross-referenced pictures and text snippets on the book (here's a fairly random sample). And that struck me as rather similar to the way translators have to read as we work on texts. Get to description of place/person/thing, attempt to visualise, research if visualisation not possible, search own memory/dictionary/web for appropriate translation, insert into text. Continue.
And now you can do just that the easy way with Berlin references in certain books. OK, only ten books right now, but there's room for more if they get the funding. Landvermesser.tv is a website that combines Google Maps with videos of authors talking about the places where their Berlin books are set, with extracts and downloads and actual GPS-based tours that you can hire out if you happen to have a spare afternoon in Berlin. Apparently there are five concrete blocks around town too that start off the videos automatically when you walk past them. I wouldn't know, as I don't get out much. My favourite, of course, is Ulrich Peltzer, who talks about his surveillance/resistance novel Teil der Lösung and some of the places around Kreuzberg where it's set. Very caustic.
On a slightly lower-tech note, you could also go on a Literatour around Berlin courtesy of the excellent website Literaturport. Also using Google Maps, here you can download authors giving you a tour of their Berlin as an mp3 file and follow in their footsteps, or just read the texts and look at the photos. Enjoy that Julia Franck tour I mentioned a while ago, for instance, or explore historic Brandenburg with Günther de Bruyn. I might well get round to the one by Katja Lange-Müller, which ends in a pub. They also have a kind of Google Earth/Google Books-style option that won't make your computer overheat - under Literatur zum Ort you can choose a part of Berlin and Brandenburg (the bit of Germany around Berlin) and they'll give you not just little quotes but page-long pieces of out-of-copyright literature referencing that place. Someone must have spent years finding it all. With all sorts of other weird and wonderful things to discover, this is another gem of a German-language site.