The morphological dimension
INTRODUCTION
This chapter is in three parts and focuses on the 'morphological' dimension of urban design; that is, the layout and configuration of urban form and space. There are essentially two types of urban space system, which, for the purposes of this book, will be referred to as 'traditional' and 'modernist' (Box 4.1 ). 'Traditional' urban space consists of buildings as constituent parts of urban blocks, where the blocks define and enclose external space.
'Modernist' urban space typically consists of free
standing 'pavilion' buildings in landscape settings.
During the modern period, the morphological structure of the public space network has changed in two important ways (Pope, 1 996; Bentley, 1 998):
from buildings as constituent elements in urban blocks (i.e. connected terraced masses) defining 'streets' and 'squares', to buildings as separate free
standing pavilions standing in an amorphous 'space'; and from integrated and connected small
scale finely meshed street grids, to road networks surrounding segregated and introverted 'enclaves'.
In each case there is currently a reaction to these changes. The changes are discussed in the first and second parts of this chapter. The final part discusses urban blocks and urban block structures. Before that, it is necessary to present a more general discussion of urban morphology.
URBAN MORPHOLOGY
Urban morphology is the study of the form and shape of settlements. Appreciation of morphology helps urban designers to be aware of local patterns of development and processes of change. Initial
work in the field focused on analysing evolution and change in traditional urban space. Morpholo
gists showed that settlements could be seen in terms of several key elements, of which Conzen (1 960) considered land uses, building structures, plot pattern and street pattern to be the most important. He emphasised the difference in stabil
ity of these elements. Buildings, and particularly the land uses they accommodate, are usually the least resilient elements. Although more enduring, the plot pattern changes over time as individual plots are subdivided or amalgamated. The street plan tends to be the most enduring element. Its stability derives from its being a capital asset not lightly set aside; from ownership structures; and,. in particular, from the difficulties of organising and implementing large-scale change. Changes do happen, however, through destruction by war or natural disaster or, in the modern period, through programmes of comprehensive redevelopment.
The following sections expand on Conzen's four morphological elements. The varied patterns and environments that these form can be studied through what Caniggia terms tessuto urbana or 'urban tissue' (Caniggia and Maffei, 1 979, 1 984).
Land uses
Compared with the other key elements, land uses are relatively temporary. Incoming uses often lead to redevelopment and the creation of new buiild
ings, to plot amalgamations and, less often, to subdivisions and changes in the street pattern. By contrast, displaced land uses are more likely to relo
cate to existing buildings in older areas and, rather than redeveloping them, to adapt and convert them.
61
62 Public Places - Urban Spaces
Building structures
Plots have often had a recognisable progression or cycle of building development. In England, this process transformed the medieval 'burgage' plots, which started out as long, narrow fields laid out perpendicular to a street or circulation route (Conzen, 1 960) (see Box 4.2). Because the first part of a plot to be developed was that adjoining the street, development generally began in 'perimeter
block' form. Loyer (1 988) describes similar devel
opment and urban intensification in eighteenth and nineteenth century Paris, and the cycle also holds true for nineteenth century industrial towns and twentieth century suburbs (Whitehead, 1 992).
With no indigenous tradition of burgage plots, many New World countries witnessed an early focus on grids: Moudon (1 986) details the evolu
tion of block, lot and building patterns in San Fran
cisco's Alamo Square neighbourhood.
Some buildings - churches, cathedrals, public buildings, etc. - will last longer than others for a variety of reasons, including the greater investment - financial and symbolic - in their design, construc
tion and ornamentation. Such buildings may also become particularly meaningful to residents and visitors, and often symbolically represent the city.
In the absence of conservation controls, other buildings survive only if they are able to adapt to new or changing uses: that is, if they have a qual
ity known as robustness (see Chapter 9). Buildings that endure over time often accommodate various uses and/or intensities of use during their lifetime - for example, a townhouse may successively be an upmarket single-family home, then offices, then student bedsits.
The plot pattern
Cadastral units (urban blocks) are typically subdi
vided or 'platted' into plots or lots (Figure 4.1 ).
These may be 'back to back', each having a frontage onto the street and a shared boundary at the rear. Plots may also face onto main streets at the front with service alleys at the rear. Less common are 'through' plots with a frontage onto
The morphological dimension �13
'�
4
�
5n
Urban fallow
a main street at each end. Over time, as plots are bought and sold, boundaries can change. Larqe plots may be subdivided, or several may be amal
gamated. As plots have been amalgamated to enable the construction of larger buildings, plot sizes have become larger. This process usually occurs in one direction only: plots are often amal
gamated, but more rarely subdivided. In extreme cases, such as the construction of shopping centres in central areas, whole urban blocks can be amal
gamated, with any intervening streets being priva
tised and built over. Although plot and block amalgamation removes most of the evidence of earlier forms, in many towns, especially in Europe, evidence of earlier plot patterns persists from that period. As few of these plots have buildings of that period, it also demonstrates that buildings chanqe more rapidly than plot patterns.
The cadastral (street) pattern
The cadastral pattern is the layout of urban blocks and, between them, the public space/movement channels or 'public space network' (see below).
The blocks define the space, or the spaces define the blocks. The ground plan of most settlements
64 Public Places - Urban Spaces
can be seen as a series of overlays from different ages. The term 'palimpsest' is used as a metaphor for such processes of change, where current uses overwrite, but do not completely erase, the marks of prior use. Twentieth century roads often cut through the street patterns of older areas, leaving
FIGURE 4.2
The street pattern of central Florence retains the layout of the original Roman settlement (source: adapted from Braunfels, 1 988)
FIGURE 4.1 These buildings in central Prague show the evidence of their original long narrow plots fronting onto a public space
fragmented townscapes. Patterns of streets and spaces have often developed over many hundreds of years, and fragments and 'ghosts' of patterns from different eras can be seen in the g round plans of many cities. In Florence, for example, the Roman street pattern is still evident in the plan of the city's central core (Figure 4.2).
An important urban design quality established by the cadastral pattern is that of 'permeability' - meaning the extent to which an environment allows a choice of routes both through and within it. It is also a measure of the opportunity for movement. A related measure - 'accessibility' - is a measure of what is achieved in practice (i.e. a prod
uct of the interaction between the individual and the cadastral system). 'Visual' permeability refers to the ability to see the routes through an environ
ment, while 'physical' permeability refers to the ability to move through an environment. In some cases there may be visual but not physical perme
ability (and vice versa).
Cadastral patterns composed of many small
sized street blocks have a fine urban grain, while patterns with fewer larger blocks have a coarse urban grain. An area with smaller blocks offers a greater choice of routes and generally creates a more permeable environment than one with larger blocks (Figure 4.3). Smaller blocks also increase visual permeability - the smaller the block, the easier it is to see from one junction to the next -
f- 1 "" I'
L � L_
L '
\. /
"' /
/ _,
"<" I
....v -v 'v v
thereby improving people's awareness of the choices available.
A basic distinction in cadastral patterns can be made between regular or 'ideal' grids characterised by geometric regularity and organic or 'deformed' grids characterised by apparent irregularity.
Although in terms of physical permeability, the shape of the grid does not matter, deformities may affect potential movement by reducing visual
permeability (see Chapter 7).
In countries and regions with a long history of incremental urbanisation, most urban grids are 'deformed' (Figure 4.4). They are often described as 'organic'; their layouts having been, or appearing to have been, generated naturally rather than being consciously manmade. Generally based on pedes
trian movement, and strongly influenced by local topography, they were built as integral parts of the immediate area rather than as through routes, and evolved and developed with use. Bill Hillier (1 996a, 1 996b; Hillier et a/., 1 993) has extensively theorised the relation between movement and the evolution of the urban grid. His central proposition is that movement largely dictates the configuration of urban space, and is itself largely determined by spatial configuration. The theory's principal genera
tor is that, considered purely as a spatial configura
tion, the urban grid's structure is the 'most powerful single determinant' of urban movement (Hillier, 1 996b, p. 43) (see Chapter 7).
Regular and ideal grids are usually planned and typically have some degree of geometric discipline.
Due to the ease of laying out straight streets, the
/ I I'
The morphological dimension �;5
I' ....!>
_:,.
-'> ,
FIGURE 4.3 Permeability. Finely meshed grids offer many different ways to get from place to place within the grid. Coarser
'v 1/ ' v
grids offer fewer ways. If the grid becomes discontinuous through the severing of connections and the creation of dead ends, permeability is reduced.
This has radical impacts within coarsely meshed grids
most basic planned layouts have generally been rectilinear. Many European cities have as their foundation Greek or Roman regular or semi-regular grid plan settlements. In Europe, regular grid
FIGURE 4.4
Plan of Rothenburg, Italy. In a 'deformed' grid, the structure of the space is deformed in two ways. First, the shaping and alignment of the islands of buildings (i.e. urban blocks) mean that sight lines do not continue right through the grid from one side to the other but continually strike the surfaces of the building blocks.
Second, as one passes along lines, the spaces vary in width. Hillier (1 996) argues that 'deformities' in the grid affect visual permeability and are, thereby, an importotnt influence on movement (source: Bentley, 1 998)
66 Public Places - Urban Spaces
patterns have frequently been overlaid on, or added alongside, more organic patterns, for exam
ple by Cerda in Barcelona. Various cities in the New World are examples of regular, orthogonal g rids, by which large, relatively plain tracts of land could be easily divided into manageable plots and sold off.
The grids used to lay out cities in the US became simpler over time. The public squares and diagonal streets that constituted important features of earlier street patterns - in Savannah, Philadelphia, Washing
ton, etc. - were often dropped later in favour of simpler systems of straight streets and rectangular blocks. Noting that few American cities used the grid
iron as 'more than an equitable expedient', Morris (1 994, p. 347) regards Savannah as an important exception and suggests that the urban mid-west's geometry might well have been 'less monotonously debasing' under its influence (Figure 4.5).
Some planned street patterns have an important symbolic function written into the overall plan.
Traditional Chinese capital cities, for example, were planned as perfect squares, with twelve city gates, three on each side, representing the twelve months of the year; Roman new towns had two intersect
ing main streets representing the solar axis and the line of the equinox. Such layouts are not always religious or ancient. In Washington DC, for exam
ple, the locations of the White House and the Capi
tol symbolise the separation of executive and legislative powers.
While deformed grids usually have a picturesque character as a result of their changing spatial enclo
sure, regular grids have often been criticised for their supposed monotony. Camillo Sitte (1 889, translated in 1 965, p. 93) condemned Mannheim's 'unrelenting thoroughness', where there were no exceptions to 'the arid rule that all streets intersect perpendicularly and that each one runs straight in both directions until it reaches the countryside beyond the town'. Rybczynski (1 995, pp. 44-5) argues, however, that such grids do not necessar
ily lack poetic character: picturesque elements occur where, for example, grids meet the natural landscape, as in the fracturing of the grid by ravines in Los Angeles. Equally grids do not have to be homogeneous and entirely regular. The 1 81 1 plan of midtown Manhattan, for example, had broad, short-block avenues for large buildings, and narrow, long-block streets for smaller row houses, while open squares, wider avenues, and in particu
lar the meander of Broadway, introduced elements of differentiation and interest.
FIGURE 4.5
Savannah was laid out on the basis of cellular units with growth intended to be by repetition of those units. Each unit had an identical layout: four groups of ten house lots and four 'trust lots' (reserved for public or more important buildings) surrounding a public square. The main through traffic was on the streets between cellular units, leaving the public squares to quieter traffic. At intervals, tree-lined boulevards, replaced ordinary streets (source: adapted from Bacon, 1 967)
During the late nineteenth and early twentieth centuries, in many countries (especially the USA) the dominance of rectilinear patterns provoked reaction against their use in favour of continuous curvilinear layouts, where wide, shallow plots (in contrast to deep, narrow ones) offered an impression of spaciousness. Curvilinear layouts derived from English picturesque design of the early nineteenth century, such as John Nash's 1 823 design for Park Village near Regent's Park, are exemplified in Olmsted and Vaux's 1 868 plan for Riverside near Chicago, and Letch
worth Garden City (1 905). While curves served to enclose views and add visual interest to newly devel
oping neighbourhoods and suburbs, they were also designed to reduce visual permeability and discour
age non-residents from entering into the area.
Most of the curvilinear patterns developed from the late nineteenth century through to the 1 920s and 1 930s were variations of g rids. A refinement (introduced by Unwin and Parker at New Earswick, 1 898) which became increasingly common during the late 1 950s, was the cul-de-sac. Cui-de-sacs sought to retain the aesthetics of curvilinear layouts while militating the nuisances and dangers of cars and other traffic such as the problems of through traffic. As is discussed later in this chapter, wide
spread use of this road form changed the public space network from a grid to a hierarchical and discontinuous pattern.
THE PUBLIC SPACE NETWORK AND THE CAPITAL WEB
The cadastral pattern establishes an urban area's public space network and is a key element in the broader concept of the capital web (see below). As well as displaying and providing access to the 'public face' of private property, the public space network accommodates the overlapping realms of 'movement space' and 'social' space (i.e. outdoor space for people to engage in economic, social and cultural transaction). This social space is a constituent part of the 'public realm' (see Chapter 6). Pedestrian movement is compatible with the notion of streets as social space. Indeed, there is a symbiotic refationship between pedestrian move
ment and interpersonal transactions. By contrast, car-based movement is pure circulation. Opportu
nities for most forms of social interaction and exchange only occur once the car has been parked - prompting a focus on destinations rather than journeys.
When the principal modes of transport were by foot or by horse, the realms of movement and social space had considerable overlap. With the development of new modes of travel, these realms have become increasingly compartmentalised into vehicular movement space and pedestrian move
ment/social space. At the same time, public space has been colonised by the car and the social aspects of the 'street' suppressed in favour of movement and circulation - the 'road'.
The pattern of blocks and the public space network, plus basic infrastructure and any other relatively permanent elements of an urban area, constitute the above ground, visible elements of David Crane's 'capital web'. For Buchanan (1 988a, p. 33), the capital web 'structures a city, its land uses and land values, the density of developments and the intensity of their use, and the way the citi
zens move through, see and remember the city as well as encounter their fellow citizens'.
In working within the capital web, urban design
ers need to be aware of patterns of stability within change: that is, to differentiate between elements which either do not change or change slowly (giving a measure of consistency of character and identity) and those that change over much shorter periods of time. Buchanan (1 988, p. 32) argued that it was the movement network, the services buried beneath it, and the monuments and civic buildings within and adjacent to it - plus the images these structured in the mind - that formed
The morphological dimension 67 the relatively permanent parts of the city. Withiin this framework, individual buildings, land uses and activities come and go. Hence, even thoug1h subject to change, some essence of the city's iden
tity is retained (see Chapter 9).
BUILDINGS DEFINING SPACE AND BUILDINGS IN SPACE
A major transformation in the morphological struc
ture of the public space network was from build
ings as constituent elements in urban blocks - i .e.
terraced masses, defining 'streets' and 'squares' - towards buildings as freestanding pavilions in amorphous space. According to Modernist 'func
tionalist' ideas, the convenience of a building�'s internal spaces was the principal determinant of its external form. Le Corbusier (1 927, p. 1 67), for example, likened a building to a soap bubble: 'This bubble is perfect and harmonious if the breath has been evenly distributed and regulated from the inside. The exterior is the result of interior.' Designed from the inside out, responding only to their functional requirements and to considerations of light, air, hygiene, aspect, prospect, 'move
ment', 'openness', etc., buildings became sculp
tures, 'objects in space', their exterior form - and therefore the relationship to public space - merely a by-product of their internal planning.
At the larger scale - and based on ideas of providing healthier living conditions, of aesthetic preference, and of the need to accommodate cars in urban areas - Modernist urban space was intended to flow freely around buildings rather than to be contained by them. Le Corbusier, for example, saw the traditional street as 'no more than a trench, a deep cleft, a narrow passage. And although we have been accustomed to it for more than a thousand years, our hearts are always oppressed by the constriction of the enclosing walls' (quoted in Broadbent, 1 990, p. 1 29). The desire for separation was reinforced by publlic health and planning standards such as density zoning, road widths, sight lines, the space required for underground services, street by-laws and daylighting angles.
The shift towards freestanding buildings was also fuelled by the desire for them to be distinctive - a consequence of the commercial interests of the development industry and building sponsors.
Buildings can stand out in a number of ways, such as by being physically separate or taller than