Andrew Smith wrote:
"IIRC, Juan Alayo was looking at calculating the amount of business
opportunities and street frontage available within certain constraints:
M changes in direction, N minutes walk, etc.  As I recall, these were being
built into the "City Matters" model, though I'm afraid that I rather lost
track of where that model got to: can anyone here provide an update?"

Andrew, 

An update from the source itself, a "silent" (until now) reader of this
list, and my greetings to a number of people that I see contributing
regularly and may remember me from the old days back at the Space Syntax
Unit (1988-1990).

Yes, one of my main areas of interest over the years has been not just
density per se, but how that density is made up (the mixture of uses) and
how it is distributed over the urban network.  Primarily to be able to
derive some type of pedestrian accessibility measure that could be useful at
the planning stages.

I developed a tool (the CityMatters model) to help me play with these
parameters and quantify at least some of these accessibility aspects.  That
tool is really a prototype and has not developed much further than what you
saw when you were at TfL. It is a segment and node model where the two
relational properties are line of sight (axiality) and physical distance
(the network has a real scale).  The segments and nodes can have the amount
and type of land use coded in as an attribute, which are then used in the
calculations.  The calculations offer a mix of "traditional" space syntax
measures, like integration, others related to actual physical distance and
hybrids.  Having said that, to achieve detailed land use data for any area
proved a very difficult task.

I must say that having seen recently some initiatives for a collaborative
effort in software development I've been tempted to chip in, but I don't
think I can find the time just now.

Having provided an update on CityMatters I'd like to contribute with a
couple of thoughts on the topic at hand.

In a sense, we are discussing the differences between acessibility and
movility.  At the risk of sounding too simplistic, if you can increase your
movility, in terms of how far you can reach given a certain amount of time,
the range and amount of destinations available typically increases and you
can therefore afford to go and live in a "less accessible" place, still
maintaining adequate levels of accessibility for you.  In a fully dispersed
ideal environment (Broadacre City?) this might be so, in reality with
congestion, parking restrictions or publict transport limitations
(frequencies, cost, etc) this normally only works for a few.

A number of years back, I derived from the National Travel Survey an
interesting statistic, that, if I recall correctly, implied that, in the UK,
about 40% of the population were the drivers for about 90% of the car
journeys.  This is a different way of saying that there is a very large
minority that can't drive because they don't have a licence and some more
that can't because even if they had a licence they don't have access to a
car. Significantly, professionals and decision makers tend to be
predominantly in that 40% doing the driving.

And this to me is the key. We may have cheaper cars in the future, and very
clean too, but I doubt we'll ever have universal access to a private
transport mode (kids, old and frail people...).  On the other hand, walking
is the most "accessible" mode of transport and if we could plan our cities
so that most people (not just those who work) could have access to a broad
(and varied) enough range of facilities or destinations on foot, then
mechanised transport could well become a secondary issue.

I suppose that, in essence, that's why I find important being able to
measure pedestrian accessibility for the various land uses and keep reading
this mail list.  

Juan