Tom Dine raises so many interesting questions that it is difficult to
respond in one piece of prose, so for the bulk of this I'll fill in some
responses to points in the text as they occur to me. Why the axial line? is
a very good question, and one to which I think there is no single fixed
answer as yet (though I think we are beginning to get somewhere with this -
more of which in a bit). What is an axial line? is actually fairly well
specified - to the point that computer software can draw axial maps given a
vector based map of the environment. Axial line drawing rules as they are
described to researchers (humans) run somthing like 'draw the set of longest
straight lines that connect all convex portions of space and make all
circulation rings. Enough lines should be drawn to minimise steps of depth
between any other pair of lines.' The way the computer programme works is to
draw the all line map in which every line tangential to a pairs of convex
vertices, or originating in a concave vertex and tangential to a convex one,
or joining a pair of concave vertices, in the environment is drawn and
extended as far as possible (these are all canditate 'longest lines'). As it
stands the all line map is a useful analytic tool, but computer processor
hungry. For this reason we still tend to use fewest line maps, and humans
are so good at drawing these, that we tend just to use the 'rule and the
ruler'. The reduction to fewest line maps by computer has been demonstrated,
but not mathematically proven to function for all possible configurations -
that kind of proof is difficult.
Tom is quite right to question the assumptions made by the cartographer and
the features represented on the map. Cartography usually does not have
syntax analysis in mind, and does not necessarily represent features
consistently or clearly. Obviously, in general the answer is to check on
site if possible, and to use intelligence in deciding what constitutes a
boundary and what does not for a particular analyisis. Several questions
commonly arise: what level of resolution or granularity is appropriate for a
specific analysis? What about the difference between visibility and
permeability? What about level changes? how should stairs, ramps or lifts be
represented? The answer to these kind of questions is again to use
intelligence. Where there are two ways of doing somthing, do both and study
the differences. Syntax analysis is not magic or a formula to be followed,
it is a set of tools that can help us to understand the way that the
environment relates to other things. The key question is 'how should I
represent (and quantify) the environment in order to understand it?'
Methodology is full of choices and finding out which method tells us most is
often a crucial element of the research.
> -----Original Message-----
> From: [log in to unmask] [mailto:[log in to unmask]]On
> Behalf Of Tom Dine
> Sent: 09 February 2001 18:03
> To: [log in to unmask]
> Subject: Re: SPACESYNTAX Digest - 29 Jan 2001 to 31 Jan 2001 What is the
> Axial line?
>
>
> What is the Axial line?
>
> Reem mentions that the newsgroup has been quiet for a while.
> Well I would like to ask a few questions raised by the
> publication of articles in the British architectural newspapers
> just before Christmas. These linked a recent murder to an
> earlier analysis of the location. I was surprised by the
> antipathy it aroused in my fellow architects who used phrases
> like cashing-in on tragedy', and said that anyone could tell
> that dark corners on dangerous estates are likely scenes of crime.
My response to that is that if 'anyone could tell' why had it been designed
like that? and why had nothing been done about it? In fact the conditions
leading to the sort of social mallaise we are talking about are much more
complex than just 'dark corners' - syntax, because it can represent and
measure some aspects of spatial design, and because these aspects are found
to affect the presence of people, seems able to help us understand the condi
tions which lead to the problem, and to study whether architecture has
anything to do with it. A point that is contested by many who find it
difficult to accept that the environment can affect anything social. Is this
somehow 'bad'? My view is that those who prefer not to study these issues
are just burying their heads in the sand. But what would we be if in
studying them we found somthing out that might help alleviate the problems
or avoid them in the future, and than failed to communicate the findings?
That would be socially irresponsible.
>
> As my friends know I have an interest in Spacesyntax, I am
> expected to defend it, but I still have difficulties with some of
> the basics. Since I last raised similar questions on this
> newsgroup two years ago I have read (or re-read) the three main
> books by Hillier & Hanson and articles which some people have
> been kind enough to send to me. I have also taken the basic
> training on the software (which I appreciate is not the same as
> training in Spacesyntax). I still do not feel that I can see the
> essence of spacesyntax.
>
> The complaint that I hear, particularly by those who have some
> acquaintance with Spacesyntax, is that the computer graphics are
> there to distract from an arbitrary technique - that you can draw
> lines at will and produce numbers that mean whatever you say they mean.
Well if he considers the technique arbitrary then your friend's acquaintance
with syntax is scant. Graphics are neither right nor wrong in themselves,
they can make numbers somewhat easier to understand. In investigating things
as complex as the space patterns humans build, graphics is a very useful
method of allowing one access to a lot of data at once. In the days before
computers could draw I remember taking piles of paper with numeric output
and colouring up maps by hand. The process was both tedious and immensly
instructive. It is only when you turn numbers into a visual form that
certain aspects of the analysis become clear. Of course graphics can look
just 'pretty', or 'scientific' and hide a lack of content. Architects are
used to exploiting graphics as communication media in this way. If our
graphics do that alone then they are failing. The issue of what numbers
'mean' is of course a deeper one. The thing that many find hard to
understand is that syntax is not just a method leading to normative 'truths'
(that would really be some kind of magic). The world is not like that. It is
bedded in a set of theories about society and the way that society and space
are related. Some aspects of these - specifically those about how space can
be constructed are mathematical and certain. Others - mainly those about the
effects of space on society and of society on space - are hypothetical.
These theories are testable - falsifiable in Popper's terms - and are at the
centre research debate.
>
> 1) I know lines are not drawn at will, but do they always
> represent exactly the same thing in the real world? (Is there a
> rigid protocol for extracting information from the environment? )
>
Well, it all depends on what you mean, there are complete and mathematical
protocols for constructing spatial representations and for measuring their
properties. The analytic techniques in syntax span a far wider range than
just the fewest line axial map, eg. tesselations, boundary spaces, all line
maps, overlapping convex spaces, e-partitions and visibility graphs to name
just a few. The last four are generated automatically from the vector
description of the environment (say a .dxf of a plan) and are used that way
meaning that there is less scope for differences arising from human error.
The map of the environment can define any boundaries the researcher
chooses - boundaries to visibility, to permeability, to both, small kerbs
can be a barrier to the disabled, 2m walls may not be to the thief.
When you ask whether they represent the same thing in the environment, I
would say not. They are tools to be used by a researcher to understand
somthing and can be applied in a wide range of ways to ask different
questions. For example, axial maps can be used to represent vehicular
networks and pedestrian networks in the same city. The maps would be
different, and the interpretation of their results would no doubt differ as
well. The fact that they use a common framework allows the analyses to be
brought together and for hopefully intelligent questions to be asked about
the interactions between the two travel modes.
> 2) I know the statistics are not arbitrary, but do the
> spacesyntax measures represent some inherent features of the
> environment with relevance to human life?
>
> The first concern relates to the fact that the impressive
> computing only applies after axial maps have been drawn. Many
> architects assume that the computing is a way of extracting
> spacesyntax information out of raw environmental data, much the
> same way that daylight programs take data about solid walls and
> windows and tell you about brightness . In exercises on the
> Spacesyntax software we used pre-existing maps on which to draw
> lines. I presume this is not how proper analysis is done,
> because we cannot be sure what features of the environment were
> recorded by the cartographer. If you draw a new map specifically
> for spacesyntax analysis, what features of the environment do you
> record, and how do you measure them?
>
> This brings me to my second concern; in spacesyntax analysis one
> derives various statistics, which correlate with human behaviour
> patterns. Surely this must be because they reflect something
> noticeable in the world, even if it is perceived subconsciously.
> After all, perception is the_only_mechanism which connects human
> behaviour to the environment it occurs within. Most of the
> spacesyntax literature I have read describes only environmental
> features (such as 'connectivity') without mentioning
> the_significance_that these might have (perhaps 'choice' or
> 'exploration potential' - see Ul-Haq 1999). To go back to the
> daylight analogy, I may not understand the exact meaning of lux
> levels or sky component , but I know it is all about the
> brightness of daylight in the room. I know what is being
> measured, and I know the phenomenon for which these features are
> indicators. I feel it is a lack of this sort of intuitive
> understanding which makes Spacesyntax unavailable to so many people.
I have no doubt that you are right. The problem - if that is what it is - is
that people use space intuitively and subconsciously, and so have a very
poorly developed lexicon to deal with socio-spatial issues. In this sense
space is like speech. We know that there are rules of grammar, and we use
these everyday to make ourselves understood and to understand others,
however we do that almost entirely subconsciously. The same goes for using
space, it is 'lawful', and we use that lawfullness without thinking about
it, so we have never named its parts. Now for syntax researchers, we are
trying to be explicit, and a large part of the effort goes into the 'naming
of parts'. This is the invention of a technical jargon, and just like any
technical jargon its job is to allow those in the know to converse
unambigously. The problem is that for the lay public it is just that -
jargon. We do our best to use words that convey somthing of the everyday
meaning associated with some concept (although that in itself is a risky
thing to do), thus Integration and Segregation probably convey somthing
close to what they measure about a spatial system. The same for
'intelligibility'. But in each of these cases there is a precise
mathematical meaning to the 'jargon' version of the word. This is a bit like
'brightness'. The problem is that the concepts we are trying to talk about
unambiguosly are often both more complex and less tangible than
'brightness', or 'segregation'. They might be effects of buildings on
'organisational culture' for instance, where pinning down exactly what is
meant by culture is difficult in its own right. I content myself in the
belief that space syntax papers are a model of clarity compared to anything
written by Lacan or Derrida or any of their followers.
>
> I can see that these two concerns are closely linked: If we are
> clear about the human significance of the features we are
> measuring, then we can be clear about what to record and how to
> measure it. Saif-ul- Haq was kind enough to send me his paper
> "Can Space Syntax Predict Environmental Cognition?" which makes
> the interesting point that the features which are significant for
> the behaviour of strangers are different to the features which
> are significant to those acquainted with the space. He notes
> that connectivity is attractive to strangers since it indicates
> exploration potential , but the ONLY relevant connections are
> those which can be seen from the entry-point. The significance
> of this measure is intuitively understandable, and the protocol
> for measuring it is made clear; if you can t see it you don t count it.
>
> 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? There is also the question of the variety of
> hazards to movement along a road, such as busy side-streets which
> might be seen as partial obstructions to movement.
Well - in the light of what I've said above, it should be clear that a curve
can be represented by a direct connection, if that is what you are trying to
represent, and so long as you are being consistent. The question is, if I
represent it one way (direct connection) or another (broken up somehow)
which version of the analysis tells me somthing interesting (for instance,
which correlates best with an observed human behaviour or what ever). The
choice of representation is part of the analysis, but the empirical data
about the world 'talk back' and tell you which one to think about. This is
just the beginning of course. If, say, the connected version correlated best
with movement, you are now left with a new and more interesting question,
that is 'why?'. This is why I think the question 'why the axial line?' is
the more interesting question.
>
> 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. 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.
>
> 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?
Well, you are describing pretty much exactly what we have found empirically
to best predict movement in cases of the sort you describe. The actual path
deviates, but you can see the whole from wherever you are. In these cases
the axial representation that correlates the best is usually the one that
maps it as a single line. The research approach is to map it both ways and
see which correlates best. By the time you have done this many times and
observed the same result - the simplified 'visual' line correlates best -
you have an interesting question to answer - 'why?' what does this finding
tell us about how people understand the world? Why is it that metric
distance does not seem to matter so much? etc.
>
> Who s axial line is it anyway?
>
> As Ul Haq has shown, it is important for strangers, and perhaps
> also acts as a location check for those more familiar with the
> place. But surely it is not the most important feature of
> spatial configuration for locals? Anyone who has visited Venice
> or Lindos will be familiar with a strange non-visual knowledge of
> routes which you can develop where the lack of cars allows paths
> to be continuous whilst twisting continually. A direct route
> becomes a path with no difficult choices, regardless of its twists.
>
> It might therefore be valuable to develop a measure of continuity
> for pedestrian routes, accounting for steps, gates, suddenness of
> change & simplicity of route. I am thinking here of Alasdair
> Turner s paper last year "Angular Analysis: a method for the
> quantification of space" as at least a partial answer. I would
> also like to consider the degree of observation possible along
> the path again Venice offers many oblique views across canals
> to the next part of the same path, some partially obscured by
> high bridges. Perhaps human understanding of space might be
> further described by good routes , with goodness measured by
> degrees of obstruction to movement and to sight-lines. There
> might even be sub-categories of visible routes and walkable
> routes reflecting the domination of visual or ergonomic continuity.
Nice ideas, and very close to the current research where we are developing
computer agents with vision to test out these kind of issues.
>
> It is clearly right that the relative position of a space within
> a configuration of spaces is important to how human life works
> within the space (often described as how the space works ).
> Depth seems to be one of those intuitively meaningful
> descriptions of space as used by humans. What I want to
> understand is what sort of thing is the axial line that describes
> depth? Is it depth for strangers ? would a map of minimum
> walkable routes reflect depth for locals ? Ul Haq s study
> suggests that the functional effect of depth reflects the
> decisions people make as the work through a spatial complex,
> being affected by the choices available at particular points and
> those which appear to be ahead (even when these might lead them
> off the shortest path). A maze seems deeper than a grid of the
> same axial depth , and surely affects behaviour differently.
These are all clearly research questions, that the method allows one to
address. (By the way, a grid is by its nature very shallow half the spaces
directly connected the rest one step away. Mazes tend to be deeper) having
said that, it is possible to construct 'unintelligble' gridy structures and
'intelligible' deep structures.
>
> So; would it be correct to say that the axial line answers the
> question "can you see where you are going and how to get there"?
> Perhaps a view from a hilltop over a winding road decending
> might meet this criterion. But of course, an axial line is
> always part of an axial network perhaps it just asks "can you
> see a point on your route and how to get there?" This would
> suggest that you need to be able to distinguish one point from
> another. I recall a sense of getting nowhere when walking
> through Milton Keynes because everywhere I fixed my attention
> looked the same.
>
My view, which I am trying to formalise at the moment in a paer for the next
Syntax Symposium, is that the axial map is a representation that results
from integration of multiple viewing locations - ie. as you move. In this
sense it captures movement directly.
> Another network property would be "how much choice can you see
> ahead?" For those familiar with the area it might be more
> relevant to ask "how much route-choice do you _know_ to be
> available?". Similarly, how complex do you _know_ the route to be?
>
> In struggling towards some understanding of what the axial map is
> all about (what phenomena it indicates) I have found the following items:
>
Destination views (or depth of view)
>
Route view complexity
>
Apparent choice (or exploration potential)
>
Route choice
>
Route complexity
>
> These seem to be (more or less) represented respectively by:
>
Axial lines
>
Axial depth
>
DP degree
>
Ringiness
>
Angular depth
>
> I would be very interested to hear from those who know, whether
> these seem to make sense or have I missed the point?
All make absolute sense - you should read Ruth Conroy's PhD which tackles a
lot of these issues and develops some measures particularly about route
choice.
>
> I appreciate that natural movement is about more than
> wayfinding, and that spacesyntax is about more than natural
> movement. There are other issues here, such as the influence of
> social control on the movement through a spatial complex, perhaps
> for another time.
>
Time for a plug for the MSc AAS - this is a nice way to spend time
investigating these issues :-)
Alan
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