Do you remember what you were doing a year ago today? Daniel Giovanni does. A social media specialist in Jakarta, Indonesia, he recently began using a clever service called 4SquareAnd7YearsAgo. The service plugs into your Foursquare “check-ins” — those geotagged notes showing where you ate, drank, and socialized. Each morning, it finds your check-ins from precisely one year earlier and emails you a summary.

The result is a curiously powerful daily jolt of reminiscence. I talked to Giovanni on July 20, the one-year anniversary of his thesis defense, as he looked over the check-ins for that day. According to the recap, he arrived on campus at 7:42 am to set up (with music from Transformers 2 pounding in his head), left the building at 12:42 pm after getting an A, then hit a movie theater to celebrate with friends. Giovanni hadn’t thought about that day in a long while, but it all came rushing back.

“It’s like this helps you reshape the memories of your life,” he told me.

4SquareAnd7YearsAgo is an example of a new trend I call memory engineering — the process of fashioning our inchoate digital pasts into useful memories.

Right now, of course, our digital lives are so bloated they’re basically imponderable. Many of us generate massive amounts of personal data every day — phonecam pictures, text messages, status updates, and so on. By default, all of us are becoming lifeloggers. But we almost never go back and look at this stuff, because it’s too hard to parse.

Memory engineers are solving that problem by creating services that reformat that data in witty, often artistic ways. 4SquareAnd7YearsAgo was coinvented this past winter by New York programmer Jonathan Wegener, who had a clever intuition: One year is a potent anniversary that makes us care about a specific moment in our past. After developing the Foursquare service, his team went on to craft PastPosts, which does the same thing with Facebook activity, and it has amassed tens of thousands of users in just a few months.

“There are so many trails we leave through the world,” Wegener says. “I wanted to make them interesting to you again.”

Lifeloggers have long touted the “total recall” that’s achievable if you obsessively store and organize personal records: Never forget a thing! But Wegener has found that less can be more. When you show someone their year-old check-ins and nothing else, it’s a very crude signal — just a bunch of points on a map. But our brains seize these cues and fill in the details (even if inaccurately). It’s geolocation as a Proustian cookie.

At the moment, most memory engineering is “episodic,” focused on your personal experiences. Memolane and Patchlife, for example, take your photos, tweets, and even music listening and turn them into a scrollable diary.

But these techniques can also work with “semantic” memories of facts and info. Last winter, Amazon released a clever app called Daily Review, which takes your Kindle clippings and redisplays them for you weeks or months later — timed on a schedule that’s designed to help you absorb your reading more deeply into your brain. It’s like a book that leaps off the shelf every once in a while and reminds you of the stuff you’ve highlighted.

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