About ten
years ago, research on patterns of burglary in residential
areas, using space syntax techniques to analyse the
urban layout, suggested that burglary rates were lower
in more spatially 'integrated' streets, that is, those
with more potential movement. The results ran counter
to the fashionable consensus that 'defensible space',
with its 'strangers equal danger' mentality and its
reliance on curtain twitching residents in cul de sacs,
was the best protection against crime. Efforts to obtain
further funding for 'space syntax' research into crime
and space failed.
In 1995,
a student from Taiwan, Simon Shu, came to UCL (incidentally
giving up a Fulbright scholarship to study in the States),
determined to use space syntax techniques to make a
more exact approach to crime and space the focus of
his PhD. He had looked at spontaneous settlements in
Taiwan, and noted that the farther one went into cul
de sacs, the more one found iron locks on doors, suggesting
that remoteness from movement in public space might
be the hazard, not its presence. Showing remarkable
diplomatic skills, he secured the support and help of
two progressive police forces and set about his studies
under my supervision.
The great
difficulty in researching crime and space is that you
can only show that there are genuine effects from spatial
layout if you first take out the effects of the social
composition. As the British Crime Survey shows, there
are huge variations in crime rates from inner cities
to suburban and rural areas, and from poor to well-off
communities. In our 1980's studies, we tried to overcome
this by plotting the location of each crime exactly,
and using space syntax analysis to identify the spatial
characteristics of each location. We could then ask
if, in an area with a homogeneous population, criminals
would tend to select targets in one type of location
rather than others. Movement was a key question. Would
crime be less in spaces with less movement potential
as 'defensible space' would suggest.
In fact we
found the opposite. Figure 1 is an space syntax analysis
of one of our study areas in inner London area. Lines
are coded red for greater integration and more potential
movement through to dark blue for least integration
and potential movement. We see a clear tendency for
burglaries to be less frequent on the most integrated
lines, and more frequent on the segregated lines. This
was confirmed by statistical analysis, and shown to
be statistically 'significant'. Similar results were
found in two housing estate areas. Defensible space,
we concluded, seemed to be on the wrong track. You were
safer in spaces with more passers-by.
Figure
1 (click for a high resolution image)
An important
advantage of using space syntax to analyse crime patterns
is that the absence or relative absence of crime in
the different parts of the layout becomes as informative
as its presence. We can go beyond the usual identification
of 'hot spots', which usually turn out to have specific
social causes, and tell us little about layout. Shu
added to this a further innovation. He studied burglary
not in terms of the address of the dwelling, but in
terms of how the burglar actually gained access to the
dwelling from public space. It is no use living on a
'safe' street or cul de sac if you are in fact burglarised
from a back alley or a neighbouring car park. This meant
going back to the original police records and laboriously
reconstructing each crime in detail.
With the
help of the police, Shu chose three towns about fifty
miles from London with very different overall social
characteristics, one very affluent, another much less
so, and the third a new town. He then selected an area
within each town with a range of population types in
different sub-areas, and a full 'menu' of spatial types
- cul de sacs, through streets, footpaths, driveways,
back alleys and so on. His conjecture was that if criminals
consistently selected targets in certain types of space
in spite of the social variation, then it would be very
unlikely that this could be assigned to anything but
spatial layout.
A typical
section of a Shu map is shown in Figure 2. Burglaries
are red dots, with tails that indicate the point in
public space from which access was gained. Car crimes
are yellow dots. The first thing we note is the bottom
right burglary 'hot spot'. This is a pair of cul de
sacs originally built as edge-of-town town council housing,
now much in decline and noticeably poor. There is also
a school adjacent to the right. In other words, the
'hot spot' may well have local social causes. We also
note that the cul de sacs in question are surrounded
by a network of 'dead-end' footpaths. Most of the burglary
is from these footpaths. Shu therefore records these
as crimes committed from footpaths rather than cul de
sacs.
Figure
2 (click for a high resolution image)
Moving away
from the bottom right 'hot spot', the more diffused
pattern of burglary immediately above in the middle
of the map is much more informative. Here we see a marked
tendency for burglary to occur in the deeper parts of
cul de sacs, rather than in the 'shallow' parts that
are directly visible from the nearby through street.
If we then look at the pattern in the top left quarter
of the map, we see again that burglary is found not
on the first line of sight into the cul de sac system,
but in the deeper parts, and also on the footpaths which
link the cul de sacs. Looking to the right side of the
map, we see that the burglaries that occur on dwellings
with through street addresses are mostly accessed through
back alleys, or long driveways which conceal the house
from the street.
We can achieve
a deeper understanding of the pattern by the syntactic
analysis shown in Figure 3. The pattern of spatial 'integration'
(spatial properties which generate more movement potential)
for the layout is shown from red for most movement potential,
through to blue for least. It is quite clear that crime
migrates to the more spatially segregated parts of the
layout, where lines of sight are visually broken up
and movement potential is least. Statistical analysis
can then be used to confirm what the eye sees.
Figure
3 (click for a high resolution image)
Figure 4
then make the same analysis for a part of a second town.
In this case we find an even more striking phenomenon.
The main curving residential streets, which have greater
linearity and integration, and are lined on both sides
with dwellings whose entrances can see each other (we
say such spaces are 'continuously constituted' by dwelling
entrances, and that the houses have good 'intervisibility')
are completely free from both burglary and car crime.
Once again we see that crime migrates to those parts
of the layout where space is visually broken up, and
with least potential movement (Figure 5). Some, but
not all, cul de sacs and footpaths are particularly
at risk, mainly those where space is relatively segregated.
Cul de sacs which are more linear and 'well constituted',
are safer.
Figure
4 (click for a high resolution image)
Figure
5 (click for a high resolution image)
These results
suggest that there is no single spatial factor which
deters crime. Several factors must be present together.
On the whole, linear integrated spaces with some through
movement and strong intervisibility of good numbers
of entrances (highly 'constituted') are the safest spaces,
while visually broken up spaces, with little movement
potential and few intervisible entrances (poorly constituted)
are the worst. This is all confirmed by statistical
analysis, which also shows that you are safer from burglary
from carriageways than from footpaths, and from spaces
with good visual connections rather than from visually
isolated parts.
We cannot
then simply say that through streets are better than
cul de sacs. They can be, but it all depends on all
the other properties being present. In our third town,
for example, there are two parallel through roads adjacent
to each other, one with very high intervisibility of
dwelling entrances, the other with entrance intervisibility
everywhere broken up by long driveways with high hedges,
concealed entrances, and 'cul de sac drives' giving
secluded access to a few dwellings. The former has virtually
no crime, while the latter is a veritable crime 'hot
line'. We fully expect, then, that there will be areas
where linear, well-constituted shallow cul de sacs will
be safer than poorly constituted, visually broken up
and spatially segregated through spaces. It all depends
on how the local 'menu' of layout targets is put together.
Criminals will always select the most vulnerable locations
on offer.
These results
are of course derived from too few studies. Further
studies may bring other patterns to light. However,
the evidence we have does all point in the same direction:
passer-by help in deterring crime, more visible neighbours
is better than fewer, good visual relations to the public
domain is better than seclusion. The common ground between
these findings and current 'Secure by Design' (SBD)
guidance is the importance of natural surveillance.
The difference is that SBD seeks to achieve this wholly
from the dwelling, and actively seeks to eliminate natural
surveillance from passers by. Our results suggest that
both must be in place to maximise the security potential
of a layout.
There are
also other differences with SBD. SBD asks for small
numbers of intervisible neighbours. Our data suggests
more is better. SBD implies small-scale, inward looks
spaces. Our evidence says linear, more integrated spaces
are better. SBD seeks clear identification of each residential
space. Our evidence says visual continuity with other
spaces is better. SBD asks for symbolic 'territorial'
demarcation of the cul de sac. Our safe cul de sacs
have no such devices. On the contrary, they look like
through routes.
All of these
problematic aspect of SBD guidance come from a single
source: the 'defensible space' ideology. This leads
directly to the belief that inward looking small cul
de sacs are a better protection against crime than ordinary
street and road systems. We now know that, in some circumstances
at least, 'defensible' layouts can be particularly vulnerable.
So why was this idea adopted in the first place ? I
have heard the police complain that they were only following
what the academics told them. I think this is true.
The academic community owes the police an apology for
claiming that a simple minded nostrum could take the
place of hard research evidence and the gradual build
up of police experience.
The concept
of 'defensible space' is in any case derived from the
theory of 'human territoriality', which attracted attention
in the early seventies, but lacks credible scientific
foundation. To try to explain the huge variety of human
spatial organisation across different societies by a
single principle is in any case to seek to explain a
variable by a constant, a logical absurdity. Unfortunately,
for years 'defensible space' has created the illusion
that we know more than we do, and acted as a substitute
for proper research.
It is time
to drop the idea, and let the combination of police
experience and hard evidence that is now emerging create
the guidance that can and will make life that much harder
for the criminal. The evidence we have so far suggests
we should move on from the universal cul de sac, with
through streets only as a necessary evil - a layout
with frightening implications for the future of the
public realm of our towns and cities - and go for integrated
and 'everywhere constituted' street and road networks,
with constituted linear cul de sacs directly linked
to the through streets for the sake of variety and choice.
We must begin to design the connecting tissue of our
cities again, and populate it with those who choose
its lifestyle.
Paradoxically,
this view would be shared by many burglars. In remarkably
interesting study, Tim Pascoe of the BRE asked burglars
which type of space they preferred as targets. Many,
it turns out, liked small cul de sacs, especially if
they were visually broken up. What layout would then
deter them ? Ordinary terraced streets, they said, which
are protected at the rear by back to back gardens, and
at the front by passers-by. Burglars, it seems, do not
understand defensible space.
Bill
Hillier ( b.hillier@ucl.ac.uk)
Simon
Shu ( s.shu@ucl.ac.uk)
SPACE
SYNTAX
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