Many of the readers of this mailbase saw Alasdair Turner's amazing
presentation of Visibility Graph Analysis (VGA) at the 1999 Space Syntax
Symposium in Brasilia. For those that missed it, the paper can be
downloaded at http://www.vr.ucl.ac.uk/vga/isss.pdf.

It is remarkable, even one year on, how little discussion this presentation
has sparked within the research community. VGA marks a fundamentally new
way to measure the configuration of buildings and cities and it combines
the most useful characteristics of axiality and convexity in one
representation of space. In their paper, Turner and Penn presented stunning
findings showing the potential of the approach in predicting pedestrian
movement using graph measures. They also showed that integration values
were found to be far more powerful predictors of movement flows using a
visibility graph representation of space than when an axial line
representation was used.

Bill Hillier used to talk about 'the segment problem'. This is the problem
of how to capture the morphological cause of changes in space use along the
length of a street (e.g. differences in movement and land use from block to
block). He once suggested that a prize should be given to the person that
comes up with the methodological solution. My vote goes to Turner and Penn
for that Brasilia article. The level of detail that VGA provides allows
researchers to measure configurational properties that explain differences
in pedestrian flows not just along the length of a street but even on
either side of the pavement. Axial lines are incapable of providing a
robust description at this level of detail. Questions such as why in some
cases up to twice the number of people can be observed walking on one side
of the street than the other were not really open to rigorous investigation
before now.

At Intelligent Space, we think that this kind of approach will be so
important to the understanding of cities in the future that we have
developed a new generation of VGA software written purely in Sun's Java
language. Using the network computing power of Java, we hope within the
next few months to be able to process visibility graph analyses of entire
cities, thereby making it possible to investigate such things as movement,
rents and land uses for whole metropolitan areas with these extremely
detailed morphological measures. We are disappointed at the lack of debate
on this mailbase to this innovative approach so far, especially as there
are a number of people making interesting developments in the field (see
next message).

Wake up and smell the coffee! The future of spatial analysis has arrived.

 Here are some questions that would interest us:
-What successes or failures have people found applying VGA in empirical
studies?
-Which graph measures are most effective in VGA representations of the
built environment? (We are finding that simple connectivity is a
particularly strong correlate of pedestrian movement in urban areas).

-Is the axial map consigned to history?

Keep up the good work Alasdair, Alan and everyone at the VR Centre,

Jake


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Dr. Jake Desyllas
Partner
Intelligent Space
1 Torriano Mews
London NW5 2RZ
phone: 020 7267 7392
fax:       020 7428 0782
email [log in to unmask]
http://www.intelligentspace.com



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