Over the course of Where 2.0 and WhereCamp TFL (Tobler’s First Law) came up several times and I though it might be a good time to revisit the concept. TFL is the idea that “Everything is related to everything else, but near things are more related than distant things”. It is a simple and powerful concept. After watching the host of location aware mobile application demos at Where 2.0, especially Jeff Holden’s talk on Footstreams and Greg Skibiski’s talk on Sense Network’s analysis tool for mobile data streams, I began to wonder how this might change TFL*.

With all the streams of mobile data coming online I’ve been wondering how this might affect the basic precepts of TFL. Will a population augmented with location aware devices change some of our basic perceptions of geography? Will time become as important as space and place for geography? The vast majority of geography and GIS deals with a static world. Few of our quantitative or qualitative analysis tools deal explicitly with time, yet all around us vast data sets are being built providing detailed location and behavioral information with very fine grained time stamps. Do we have the right tools in our analytical arsenal to deal with hairy fourth dimension of time?

Amazingly this is exactly what Tobler had in mind when he developed the ideas behind TFL. The concept originated in paper by Tobler entitled “A computer movie simulating urban growth in the Detroit area” presented at the 1969 Commission on Quantitative Methods of the International Geographical Union. That’s correct a temporal simulation of urban growth presented as a movie in 1969 - pretty amazing - at least in my opinion. When there was a forum at the 2003 meeting of the AAG to discuss TFL, Tobler stated that he was “just having fun doing an animation in order to bring time into geography more explicitly”. Apparently hacking geography was producing cool stuff even back in 69′.

Tobler was influenced by physics and specifically Feynman in his thoughts about the interaction between space and time. This is interesting because physics, probably more than any other discipline, has been focused on the multi dimensionality of phenomenon. As such it is a very fertile field for thinking about how time adds a fourth dimension to geography. While much of what motivated TFL involved time it is not explicitly part of the law. Only distance is identified as a factor that causes a decay of interaction/relation.

The natural corollary would seem to be that - things that are near for a long period of time are more related than things that are near for a short period of time. I think this corollary really strikes home when we think about mobile device that are location aware. Whether we are talking about friend that are near or points of interest (POI) that are near the temporal factor is possibly more important than the spatial factor.

Let’s look back at Jeff Holden’s talk where he collected 642 days of footstream traffic with his GPS enabled device. He found that he visited Starbucks 2-4 times per day and his mean time between Starbucks was 29 hours and peaked at 12 hours in one week. Obviously there is a strong relation between Jeff and Starbucks, but I’d argue the strength comes from the duration in time he spent at Starbucks as much as the proximity of Jeff to Starbucks. I believe as the Web fully morphs into the GeoWeb - location in browsers (HTML 5), location in desktops (Windows 7), location in mobile hardware (everyone), location in mobile software (Google latitude), location hybrids (Skyhook Wireless) our understanding of the temporal dimension to all this data will become critical. Is the corollary to Where 2.0 then When 2.0?

*More generally you can read Paul Ramsey’s take here on the two talks above.

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