Sure Tao,
It is very interesting to see the effect of coast or the power laws of
urban areas in an island. Clearly, there is a geographical limit after
which large objects cannot be created.
Maybe we should make a seminar here, are power-laws power laws?
Lucas
On 01/06/07, Tao Yang <[log in to unmask]> wrote:
> Hi,Lucas,
>
> The cut-off could be also affected by the 'natural boundaries' of cities or
> subareas. Some observed cut-offs are just a function of the artificial
> boundary of a city, the size of a system, but others could reflect the
> natural character of a city, such as the extent to which communities are
> separated from each other.
>
> Best
> Tao
>
>
> Hi Hoon,
>
> That is good research question. Before, my point is: get a common
> ruler and put over most 'power laws' you see. It is not an easy
> exercise. Many cases you find a cut-off point and clear tail. Other
> cases you find 2 power-laws regimes and so on.
>
> See:
> Power laws, Pareto distributions and Zipf's law -
> MEJ Newman - Contemporary Physics, 2005 - Taylor & Francis
>
> However, many cases you do not find anything... there is no section in
> the curve that is clearly straight, and any chosen 'cut-off' point
> generates a different exponent, sometimes very different... are they
> power-laws?
>
> About your question, the power law behaviour is more clearly observed
> in the tail, 'top values'. Therefore, it is not the small chunks of
> space that will change it, but the generalisation process that creates
> the large objects (long lines in this case). If different
> generalisation processes generate different or closely related
> power-laws regimes it is a question to be addressed.
>
> In my opinion, the results can be a lot affected by the artificial
> boundary choosen in the map, the quality of the data and the
> generalisation process.
>
> Best Regards,
> Lucas Figueiredo
>
> On 01/06/07, Hoon Park <[log in to unmask]> wrote:
> > Lucas
> >
> > A question: If we include, following 'TeleAtlas' for instance, to map such
> > countless bits of space as 'The ramp to the car park at 1-19 Torrington
> > Plc' or 'The entrance to the emergency services at UCH' into a street
> > network, could it change its degree distribution from a 'log-normal' to
> > a 'power-law'? If so, can we really claim that the degree distribution of
> > street networks does not follow a power law but a log-normal?
> >
> > Regards,
> > Hoon
> >
> >
> > >On Thu, 31 May 2007 19:24:49 +0100, Lucas Figueiredo
> > ><[log in to unmask]> wrote:
> > >
> > >>On 31/05/07, Rui Carvalho <[log in to unmask]> wrote:
> > >>> Pitty no one knows what a street is...
> > >>
> > >>Certainly it is not a segment (or route) between two junctions.
> > >>Otherwise we would have things like "Oxford Street sector A, B, C" and
> > >>so on...
> > >
> > >The ramp to the car park at 1-19 Torrington Plc. This comes in GPS car
> > >navigation systems as a decision point? is it a street?
> > >
> > >The entrance to the emergency services at UCH (that's UCL Hospital for
> > non
> > >Londoners). Is it a street?
> > >
> > >This question appears when you process data from services like TeleAtlas
> -
> > >the most accurate data available on street networks...
> > >
> > >Looks like Alan should organize that 'mass observation' on what a street
> > >is after all...
> > >
> > >Comments welcome!
> > >
> > >Rui
> > >
> > >
> > >>
> > >>Regards,
> > >>
> > >>Lucas Figueiredo
> > >>http://www.flickr.com/photos/lucasfigueiredo/
> > >>
> > >>Mindwalk
> > >>http://www.mindwalk.com.br
> > >========================================================================
> >
>
>
> --
> Lucas Figueiredo
> http://www.flickr.com/photos/lucasfigueiredo/
>
> Mindwalk
> http://www.mindwalk.com.br
>
--
Lucas Figueiredo
http://www.flickr.com/photos/lucasfigueiredo/
Mindwalk
http://www.mindwalk.com.br
|