In a recent article on experiments using automatic digital photography to improve the memories of Alzheimer's patients, I was struck by these paragraphs:

When researchers began exploring it as a memory aid a few years ago, they had patients and caregivers look at all the pictures together.

Although the exercise helped improve retention of an experience, it was evident that a better way would be to focus on a few key images that might unlock the memories related to it. The interactive nature of that approach would give patients a greater sense of control over their recollections, and allow them to revisit past experiences rather than simply know they had happened.

They soon realized that the capriciousness of memory made answers elusive. For one subject, a donkey in the background of a barnyard photo brought back a flood of recollections. For another, an otherwise unremarkable landscape reminded the subject of a snowfall that had not been expected.

The idea that "the capriciousness of memory" would make efforts to automatically generate summaries of events difficult, mirrors my own experience: I have entire trips that I recall through a couple apparently random things– the look of a hotel room, what I had for dinner. Likewise, looking at an entire album of pictures doesn't necessarily do much for me in terms of helping me remember more of an event.

I wonder if the scientists have tried getting their subjects to consciously manipulate those records afterwards– to make a photo album, for example– and see if that process of sorting helps improve recall. I remember trips much better if I write about them, or choose pictures to put online, much as I remember books better when I take notes on them. In fact, it's safe to say that the ritual of going through pictures, tagging them, and uploading them has both made it easier for me to remember these places, and changed my view of the world.

Let me explain.

One of the Web services I use a lot is the photo sharing site Flickr (if you don't believe me, just go to my account and see for yourself). I'm a fairly obsessive photographer, mainly because I like good pictures, but I'm not a very good one. With a film camera, you really pay for artistic mediocrity or technical clumsiness: you have to throw the same amount of money at a good picture as a bad. With digital cameras, on the other hand, you can play the lottery: take enough pictures, and some of them will accidentally be good. I'm also a doting father whose children aren't old enough to put up a serious fight when I get out the camera. And finally, digital cameras are small enough to fit in a pocket, so my Canon PowerShot is always handy. I don't have to plan to carry a camera with me: it's one of the things I always have when I walk out the door.

One of my favorite features in Flickr is its mapper, which lets you tell Flickr where in the world your picture was taken. Essentially, you put a digital pin in an online map, much as you would in a real map. Flickr and Yahoo! Maps got together to provide the service in 2006, and since then I've become a slightly fanatical geotagger. It started out as pure geekdom: I'd written stuff about the future of geolocation services and information, so it seemed a good chance to play with a future I had already described. But now I do it because it's a way to help me remember my pictures, and where I took them.

When I'm in a place, I like to walk. I want to know enough to stay out of bad neighborhoods, to find interesting ones, and to be aware of significant landmarks. I don't want to miss the big attractions, but I also want the freedom to happen upon that perfect little cafe and pastry shop, or the brilliant bookstore that's not in any of the guidebooks. (How many travelers define themselves as people who want to escape the boundaries of the guidebooks?) This style of wandering is one reason I absolutely love certain cities. In London, for example, you can't go three blocks without coming upon something grand and historic, a charming little square, or an interesting piece of street life. You can never be sure which you'll find. It's one reason Samuel Johnson could say, when you're tired of London you're tired of life. Likewise, Singapore and Budapest reward walking, though for different reasons: Singapore is a kind of life-sized scenario of a prosperous, benevolently authoritarian, multicultural Asian Century could be like, with amazing food. Budapest is a wonderful Old European city, alternating twisty streets, grand boulevards, the magnificent Danube, and faded (but rapidly renovating) buildings and apartment blocks, with great coffee on every block.

So I like to wander. But once I'm back in my room, and have uploaded my pictures from the day, I want to reconstruct my path, and figure out where I've been. I used to do this on maps, tracing out my route with a highlighter. This wasn't always very successful. It required remembering street names, knowing how many blocks it had been since I'd turned left last, or estimating how far I'd walked on the boulevard or embankment before stopping to take those pictures. Given that I often walk at night– my days are taken up with work– all this was tough. Putting that information onto a map that often was in an unfamiliar language didn't make things easier, either.

But what turned me into a Flickr map fanatic? And what bigger lesson could that possibly hold?

The act of putting pictures on the Flickr map combines three different kinds of knowledge. First, it draws on your physical memory of travel and picture-taking. Second, it draws on your visual memory. And third, it connects those two kinds of knowledge and memory to a formal system, the logic of the map. Putting these together help you connect your personal, street-level view of a place with a higher-level, abstract understanding of it.

Consider picture-taking first. Like all forms of knowledge-creation, picture-taking is a physical activity as well as an intellectual or technical one, and that physicality can be something that helps fix in your memory the event of taking the picture. I have pictures of Wiamea Canyon, on the island of Kauai, that I can't look at without being reminded of a long drive, and the pleasant contrast between the warmth of the coast and the chilly interior. I'd probably have long forgotten those sensations without the picture, and without the sensations I'd have a harder time placing the picture; but both memories live together and reinforce each other. Often the order of pictures in a photo stream can be used to reconstruct an evening's path. Something in the distance in one picture is in the center of another, or a corner in one photo is turned in the next. With the visual cues that the photographs provide, combined with a few memories of turning down this street and that boulevard, and a couple landmarks as reference points, I can reconstruct my steps pretty accurately.

Flickr lets you put pictures on an ordinary street map, which is just a grid with street names, rivers, train lines, and the occasional park. Sometimes that's enough information; but when it's not, I switch to the satellite mode, which overlays aerial photographs atop the street map. I find that the satellite photographs let me establish much more precisely just where I was, what this photograph shows, and where it should go on the map. Without it, I can place pictures on the right block; with the satellite photos, I can get to within a few feet.

Of course, that requires knowing how to decode satellite photographs, and how to relate that information to my own experience. Figuring out how to connect what you see in your photograph to what's on a satellite picture is a skill that we didn't have to learn before. Unless you worked for the CIA or had a particularly sadistic geography teacher, you never had to make that connection; and until recently satellite photos weren't easy for ordinary people to get. You could think of the Flickr mapping tool as a giant machine that gives people the chance to learn how to read satellite pictures. Maybe it's a cartographic Ender's Game, training a generation of open-source spooks who twenty years from now won't be fooled by doctored military recon photos or what's really scant evidence of wrongdoing.

Translating the ground-eye view of a landmark or city grid into an aerial view isn't that hard, but it does need to be learned. London's Trafalger Square becomes a set of long shadows (Nelson's column) with a few shapes (the lions around it, the fountains nearby); Leicester Square, trees and park paths bordered by the blocky shapes of theatres. Sometimes you learn how big something really is ("Boy, Suntec City really is HUGE"); when I'm trying to find someplace I've reached by tai or subway, the satellite photos are the only way to find it. I've walked some parts of Copenhagen, for example, but there are some things– the new Information Technology University, for example– that I've only driven to; I don't know the ITU address, but because I know the shape of the building and have a pretty good sense of the buildings around it, I can find it on a satellite map.

Finally, putting the pictures on the map is a way to relate the personal experience and first person view to the formal, high-level view. They're my memories, organized; and organizing my memories builds my knowledge of– and arguably my understanding of– the place and how it's laid out. Given that I may post 500 pictures from a trip, and geocode almost all of them, the simple repetition of the exercise does a lot to fix in my mind what buildings are where, how places relate to each other, and what route I took when walking, say, from the Elizabeth Bridge to St. Stephen's Church in downtown Budapest.

Right now this kind of mapping is mainly fun (believe it or not) and educational, but it will really pay off in a couple years, when I can go back to city with my e-paper travel journal, equipped with wifi and GPS. So equipped, I'll be able to call up those pictures in situ: see what Piccadilly Square looked like the last time I was there, or see exactly where in Singapore I had those rice noodles so memorable I Fickred them. And I can see where I haven't been, since pictures serve as visual crumbs, dropped on the map to mark my earlier travels.