Gravity Models Circa 1846


Once in a while along comes a wonderful piece of historical research that again illustrates that in most fields, there is little new under the sun. Andrew Odlyzko’s recent paper entitled “The forgotten discovery of gravity models and the inefficiency of early railway networks” is just such a paper. In it, he shows that it was not Carey who was the first to argue that human interactions vary directly with their mass and inversely with the distances between them – Newton’s second law of motion – but a Belgian railway engineer Henri-Guillaume Desart who in 1846 (perhaps even before that date) argued that rail traffic on any new line would follow such a law. He based this on the ‘big data’ of his time, namely railway timetables and he thus joined the debate which raged for over half a century as to whether new rail lines  built point to point in straight lines with no stations between would generate more traffic than would be attracted locally if stations were clustered around big cities. This is a debate that has some resonance even today with the debate in Britain about new high speed lines such as HS2 and what stations they might connect to.

Odlyzko’s paper also notes that in 1838, a British physicist John Herapath suggested that this local law of spatial interaction for rail traffic in fact followed a negative exponential law with traffic proportional to exp(-bd) where d was the distance from some source to a station. Arguably this is an earlier discovery although it was Desart who fitted his model to data, coming up remarkably with an exponent on the inverse power of the distance in the gravity model of 2.25.

Elsewhere  I have recounted the tale of the how the Lyons electronic computer team much in advance of their time, cracked the shortest route problem in the early 1950s, several years before Edgar Dijkstra who is the accredited inventor of the algorithm. You can see the video of this here where they took on the problem of pricing freight on the British Railways network by breaking their big data into chunks of network which they needed to move in and out of store to solve the problem. In fact somewhere in the recesses of my mind, there is also a nagging thought that someone even earlier, just after Newton’s time, first applied his gravity model to human interactions. I seem to remember this was at the time of the French Physiocrats whose input output model anticipated Leontieff by more than 150 years when Quesnay devised his Tableau Economique. Old theories of social physics seem to go back to the beginnings of natural physics and although we live in a time when the modern and the contemporary swamp our history, we are gradually discovering that our human wisdom in learning to apply science to human affairs goes back to the deep past.

Geocomputation A Primer


A very nicely produced review of geocomputation in this edited book by Chris Brunsdon and Alex Singleton. It covers many interesting new techniques from agent based models to new visual statistics, from crowdsourcing methods to the newer scripting languages that are making their appearance as central to the development of contemporary spatial analysis. What is noteworthy about the book is the beautiful presentation and the visual ease in which the reader is exposed to these somewhat arcane arts of making sense of space and geography. There is a nice web site with some content that the reader can download here, and at the risk of infringing my own copyright, I will share my own chapter with you which you can download here too. Its not in the glorious presentation of the published book, merely a PDF or the word file but the figs are in colour

Coping with Disorder


….. is a short article by Richard Sennett in the LSE Cities’ programs current Urban Age magazine Governing Urban Futures. He makes the point that all the hype about big cities wanting their own governance is somewhat put into the shade by the fact that globalisation is destroying any prospects that such cities have for actually governing themselves. It’s a great little article and I won’t attempt to precis it here but there is one choice remark that I cannot resist reproducing. Towards the end of the piece after he tells us about how climate change has at least disrupted any long gone perception that we have about the fact that we live in an equilibrium world. He says:

“We should be thinking about the networks linking big cities in the same way. Specific patterns of migration are as unstable in the immediate term as changes in the natural environment; for example, movement across the Mexican-American border is an erratic, convulsive process year-on-year, though the cumulative effect is clear. So, too, is the economy of networked cities – financial flows are not smooth and linear, nor are investments in real estate or primary industry. Open system analysis thinks about networks as trembling rather than placid connections – because the connections are complex they are peculiarly open to disruption.”