"Dimensions of City Form"

Exhibit at Tallinn International Architecture Biennale

Location: Tallinn, Estonia

Date: September 2013

Project Team/Credits:  Principle Investigator, City Form Lab: Andres Sevtsuk, Project manager: Onur Ekmekci, Project Team:Martin Scoppa, Raul Kalvo, Quinn Lee Zhi Jie, Terence Teo Ling Kai, Alexandria Chong Zhuo Wen


Most daily activities of city dwellers are simultaneously constrained and enabled by the configuration of the built environment — the physical pattern of urban form, the distribution of land uses, and paths that connect them. The configuration of urban form is a generator of encounters, movements and flows, which can turn abstract geometryinto a structure filled with information. This structure generates patterns of proximity and adjacency that sort traffic on city streets, locate people and business and creates a hierarchy of places and land values. The reciprocal relationship between people and their environments constitutes a system of agreements and interactions that form a large part of a city’s culture. Anyone’s attraction towards delightful urban environments, such as Tallinn, Paris or Hong Kong, provides testimony to the important role that urban geometry plays in shaping our attitudes towards cities.

But the formal logic of a city remains poorly captured analytically. Like the grammar of a language, the structural principals of urban form are ubiquitously used but rarely examined. Kevin Lynch has proposed five performance dimensions for assessing the quality of city environments (Good City Form, 1984). His dimension of Vitality refers to the extent to which the form of the environment satisfies the biological well-being of its users.  The geographic position of a settlement, the orientation of its streets, the slopes of its pathways and the protection from the sun and rain, all contribute to the vitality of a city. Fit refers to the degree to which the buildings and public spaces correspond to the functional needs of their users. Different activities need different spaces and a desired land use mix requires a corresponding building type mix. Sense describes the degree to which the settlement corresponds to our faculties of perception and facilitates our understanding of its structure. Built environments that are easier to comprehend become part of collective memory and constitute an important aspect of people’s identity. Controldescribes how readily the configuration of the environment can be managed and modified by it users. A higher level of control allows the settlement to adapt to changing needs over time. And last, Access, illustrates how effectively the form of the environment connects its people, places and resources. Better access makes a city wealthier in opportunities. The five performance dimensions address complementary human-centric qualities in any urban settlement, but the methods for practically measuring their performance remain poorly developed. Lynch proposed a method to assessing the Sense of a place (Image of the City, 1960), but left the other four undefined.

In this exhibit we focus on Accessibility – the ease with which the form of an environment generates access to surrounding people, places and resources. Accessibility is typically defined as a combination of individual destinations around a place, and the travel costs required to reach each of the destinations. Accessibility thus depends on the number and types of destinations available, as well as the quantity and quality of the circulation paths that lead to these destinations. In order to investigate the qualities of access around a place, both paths and places need to be clearly represented. We rely on a network representation of the environment to do so, depicting all publicly accessible circulation paths with line segments, and the origins and destinations of trips with buildings and places on these paths. Such a network view of urban environments allows different access characteristics of a place to be evaluated using spatial network analysis indices, illustrating the outcomes graphically on maps.

The exhibit introduces a set of metrics that can be used to capture qualities of access in any city environment. Each metric captures a different aspect of accessibility by either focusing on the availability of destinations, the travel costs of reaching the destinations or on the characteristics and choices of available paths. We explore the use of five different metrics – Reach, Gravity; Betweenness; Straightness and Redundancy. Each metric is explained and illustrated individually. The metrics are specified for individual buildings, businesses, entrances or transit stations in the case study areas and the variation in their accessibility outcomes compared within and between case-study sites.

These accessibility metrics are not merely abstract mathematical representations of urban configuration; they have been carefully developed to capture human perception of access in city environments. Each metric describes behavioral opportunities and constraints that a given configuration of urban form produces. We couple each metric with a set of hypotheses that suggest how the variations captured by the metric affect the social or economic functionality of the environments they depict. These hypotheses are explained with each metric, along with example diagrams showing how different conditions of urban form influence the metrics and produce the observed quality of space. The Betweenness metric, for instance, can be used to estimate the amount of passing traffic or footfall on different circulation paths of a district. A greater amount of footfall, in turn, can lead to a greater density of commercial uses along these routes. Each hypothesis is then explored with a series of photographs illustrating how the case study environments look and feel like at places where the metric is high and at places where the metric is low.  The location of each photo is shown on the corresponding measurement map.

Investigating the access properties of the case study environments with the four metrics also poses important questions about what we should expect. What is a “good” distribution of Betwenness measures in a neighborhood? How much redundancy in path choices is desirable? Thought it is indeed important to ponder over these questions for any designer or policy maker, there is no correct answer. Each place can have its own “good” balance of accessibility characteristics. We do suggest, however, that a more diverse distribution of the measures is generally beneficial. Environments that generate more diverse qualities of access – high levels of access in some buildings and poor levels in access in others– make different parts of a district suitable for different activities and different users. Spatial diversity generates unplanned encounters between people and places, making the users of an environment more aware of each other.

Two districts in Singapore – Bugis and Punggol are used to test the ideas on contemporary city fabric in Singapore. In two surveys during the fall of 2012, researchers from the City Form Lab mapped three layers of information in a ten-minute walking radius around the Bugis MRT station and the Meridian LRT station in Punggol. The maps, shown at the exhibit, document 1) the ground floor structures of all load-bearing walls in buildings, 2) the distribution of all economic establishments in the areas (marked by their doors and described by a series of attributes) and 3) the outdoor and indoor pedestrian circulation networks that are accessible to the public. Additionally, the Publicness of each of the spaces was visually assessed, dividing different places into Public, Occupiable, and Dwelling spaces. Combined, these data layers were chosen to embody complementary morphological attributes that allow the sites to be studied in great detail. The data was digitized in GIS, making it possibly to analyse and uncover the accessibility conditions of the sites using computational tools. The data allows us to describe how the environments are structured, how their activities, places and public spaces connect to each other along a network of pedestrian paths, and to analyse the mix of economic establishments encountered at different locations and on different routes.

When urbanist Peter Smithson proposed the term the “charged void” he was referring to “architecture’s capacity to charge the space around it with energy, which can join up with other energies, define the nature of things that might come, anticipate happenings... a capacity we can feel and act on, but cannot necessarily describe or record”(Smithson and Smithson 2005). Throughout this exhibit we try to argue that the charged void can indeed be described and understood. In order to describe the ‘charge’ that occupies the space between buildings and acts as a source of information for both social and spatial interventions, we need to break it down into manageable components and investigate it through questions that can be answered. We start by looking at how the charged void generates Access.


Exhibition space
Betweenness Analysis for Bugis, Singapore
One of the exhibition boards
Biennale Publication
Facebook Twitter Pinterest Flickr Instagram LinkedIn share