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.    

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.

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?  )

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 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.

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?  

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.

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.

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.

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:
Š Destination views (or depth of view)
Š Route view complexity
Š Apparent choice (or exploration potential)
Š Route choice
Š Route complexity
 
These seem to be (more or less) represented respectively by:
Š Axial lines
Š Axial depth
Š DP degree
Š Ringiness
Š 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?

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.  

regards

Tom Dine
Architect
Chassay+Last Architects
Primrose hill
London

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