Just to enter the fray - this is an email from Sheep - whose been
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>At 6:02 pm +0000 9/2/2001, Tom Dine wrote:
>>It seems to me that all spacesyntax measures are based on "what you
>>can see" and "where you can go".  However, this is not entirely
>>clear from discussions of, for instance, the axial line.  That the
>>axial line  must be straight suggests that it represents the view
>>from one point, but the fact that it ignores distance (& hills) has
>>been explained by the fact that one moves along it (Hillier 1996).
>>But a curve can also be seen in its entirety as one moves along it,
>>why can't it represent a direct connection?

Well strictly speaking a curve cannot be seen in its entirety,
imagine standing outside a large circular building like the Albert
Hall. There are problems breaking-up curves to form axial lines, this
is, I think, the key to what you are trying to describe. Perhaps
someone undertake the "distance correlates badly with observed
movement" paper once and for all, since everyone keeps suggesting it
as the ultimate measure.

>
>>Looked at in terms of "where you can go" and "what you can see" the
>>axial line might be defined as both "a continuous path for
>>pedestrian movement" and "a line of sight for pedestrians".  Axial
>>lines for car drivers would be rather different because of their
>>different rules for movement and different viewpoint.   In fact,
>>the axial line must be the coincidence of a continuous path and a
>>line of sight.  But this is not necessarily the same as a straight
>>road.


Very true! In my forthcoming paper for the space syntax conference I
have made suggestions on how we can reinterpret the intersection of
axial lines from Boolean (axial lines are connected or not connected)
to factional/fuzzy. Once computed like this we can see that lots of
little short lines following the path of an curved road no longer
have to add up to a very segregated area as in traditional
integration. (for more info on how this is calculated see
http://www.aaschool.ac.uk/sheep)

>>    In the woodland near my house there is a path which is straight
>>for some distance, but in the middle makes a series of beds through
>>marshy ground and over a little stream.  On the maps this makes a
>>series of "axial lines", but in reality I perceive it as one line:
>>the path is unbroken and I can clearly see from one end to another.

This then becomes a matter of degrees. Suppose you had a straight
line path from your house to a maze, after following the maze of some
while you emerge.  Would this produce the same result?. If there were
only one entrance and exit, then possibly. I think the simplicity of
the stream depends upon whether you have left the original 'space'.

For example if you go through one of those underground pedestrian
walk ways going under a roundabout (Old Street in London for example)
you can get terribly confused emerging at the wrong exit completely.
The only difference is the underground walk-way tends to cross back
on itself, removing any global references and views of your goal. The
real factor is whether there is a choice of routes at any stage (you
only have one for the stream route). The deviation though an
underground walk way might be the same as your little stream  but the
results would be different. How then can we cope with mapping both
the stream interruption and the subway interruption?

>
>>In cases such as this I have heard advice to adjust the map to
>>reflect the observation.  This worries me - it seems to move from
>>representing the world to representing how we want the world to be.
>>Surely  if the map reflects reality, the relevant features of
>>reality should be defined.  My reason for suggesting the above
>>definition of the axial line is to remove doubt in difficult cases;
>>we can be definite about discontinuities in a path, and about
>>limits to sight-lines.   But what about its significance?

Again, in my paper I agree with you. The suggestion in my paper is
that the solution is not as many would have you think is to improve
mapping technique. Instead I suggest that modifications to the
computational methods such as using fractional analysis will made
such map based one observation questions irrelevant. For example when
mapping New York (again see the website) it is no longer necessary to
artificially straighten Broadway.

>At 6:02 pm +0000 9/2/2001, Tom Dine wrote:
>>A "direct route" becomes a path with no difficult choices,
>>regardless of its twists.

I think that there might be more of a research issue here. One thing
we do not understand clearly from traditional space syntax is when
the visibility matrix (where I can see) and the permeability matrix (
where I can go ) differ. For example an office with half-height
partitions, or an office with glass walls.

I think for some cases (slowly curved path ways, meandering  streets
in traditional villages and towns, motorway-splines) fractional
analysis is starting to give the right answers. For the visibility
issues (such as the stream interruption) then there is, in fact, some
deeper level of understanding yet to come out. 'A "direct route"
becomes a path with no difficult choices, regardless of its twists.'
well this sounds like a rule which might be used to enhance modeling,
for me the question is can I give this to a computer program and get
the same results and I would from a human.  For a general example
think about the effects of a stair case if you do take it do you
always come out facing the direction you want?

For me the ultimate example of the visibility/permeability problem is
the change of routes people have between day and night. Street
lighting changes the visibility matrix while the permeability matrix
stays the same. Mapping this might give some deeper theoretical
insight in to this whole issue.

sheep