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augusti 13, 2004

Hur svårt är det att hitta i städer?

I Nature News-artikeln The urban maze skriver Philip Ball om två undersökningar kring hur komplicerade städer är, bl.a. en där några svenska städer (Stockholm, Malmö, Umeå) har studerats.

[Martin] Rosvall, of Umea University in Sweden, and his co-workers have tried to figure out why it is so hard for us to find our way around cities. Of course, the obvious answer is that cities have a lot of streets. And particularly if you live in an old city like London or Athens, those streets are messily arranged. But it turns out that the problem is a lot worse than that.

One way of gauging the complexity of a city is to ask how many directions you would need to get around. This need not be a function of distance: major arteries through a city can channel you efficiently between remote locations. In terms of information, any road off such a main highway is the same distance away from a particular point as any other ('second on the left' is no more complex an instruction than 'tenth on the left').
...
The real cities were consistently harder to navigate than the randomized ones, in other words the 'search information' needed on average to navigate between two points is consistently larger for real cities. There really does seem to be a property, peculiar to cities, that makes them harder to find your way around than other types of network.
...
As you might expect, Manhattan, with its chequered grid plan, proves easier to navigate than the three, less orderly Swedish cities considered (Stockholm, Malmö and Umea). But even Manhattan is more complex, by these measures, than the network formed by flights between US airports.

De två refererade papren är
Martin Rosvall, Ala Trusina, Petter Minnhagen, Kim Sneppen:
Networks and Cities: An Information Perspective
Abstract:
Traffic is constrained by the information involved in locating the receiver and the physical distance between sender and receiver. We here focus on the former, and investigate traffic in the perspective of information handling. We re-plot the road map of cities in terms of the information needed to locate specific addresses and create information city networks with roads mapped to nodes and intersections to links between nodes. These networks have the broad degree distribution found in many other complex networks. The mapping to an information city network makes it possible to quantify the information associated to locating specific addresses. We suggest a size-rescaled information measure that allows us to quantify the complexity in city organization and other complex networks.

Rui Carvalho, Alan Penn:
Scaling and universality in the micro-structure of urban space
Abstract
We present a broad, phenomenological picture of the distribution of the length of open space linear segments, l, derived from maps of 36 cities in 14 different countries. By scaling the Zipf plot of l, we obtain two master curves for a sample of cities, which are not a function of city size. We show that a third class of cities is not easily classifiable into these two universality classes. The cumulative distribution of l displays power-law tails with two distinct exponents, alphaB=2 and alphaR=3. We suggest a link between our data and the possibility of observing and modelling urban geometric structures using Lévy processes.

Se även
Complex Networks (Umeå Universitet)
NORDITA Network Research
Space Syntax.

Posted by hakank at augusti 13, 2004 09:27 EM Posted to Social Network Analysis/Complex Networks

Comments

Posted by: Lars Olofsson at augusti 13, 2004 11:11 EM

Posted by: Chadie at augusti 13, 2004 11:23 EM