Hitchhiker's Guide Meets Harry Potter's Marauder's Map

I'm standing on the vast southern lawn at Ashton Court, a stately home on the edge of Bristol, clutching a tiny electronic machine that mimics Adams's device quite eerily. It's the size of a postcard and has a small colour television screen with earphones snaking to a slot in the bottom. When I walk a few yards to my right... ping! A bell shrills in my ear and the screen bursts into life. A cheery voice declares, "You have walked into an interactive area." And what begins is a visitor experience like no other I've had. This tiny electronic prototype, called an Explorer, detects exactly where I'm standing within the 850-acre parkland surrounding Ashton Court, because it's equipped with an internal Global Positioning System (GPS) based on satellite signals, accurate to within about three yards. On screen, I see myself as a little red dot moving slowly over the grass. Depending on where I wander, an entirely different heritage or cultural story is presented through a combination of pictures, sound effects and narrative, all related to where I'm standing and what I'm looking at. I walk to the bottom of the lawn. Ping! With the sweeping fa?ade of Ashton Court spread like a film set, the screen shows me how the building has changed over the centuries, images building upon images as a voiceover explains why the place looks as it does now. (From Travel Gadgets: it knows where you are) (Node Explorer V3)

"You press this button here you see and the screen lights up giving you the index." A screen, about three inches by four, lit up and characters began to flicker across the surface. Ford pressed a large red button at the bottom of the screen and words began to undulate across it. At the same time, the book began to speak the entry as well in a still quiet measured voice. (Read more about the Hitchhiker's Guide)

But the truly remarkable thing were the tiny ink dots moving around on it, each labeled with a name in miniscule writing. Astounded, Harry bent over it. A labeled dot in the top left corner showed that Professor Dumbledore was pacing his study... (From Harry Potter and the Prisoner of Azkaban)