Introduction

In terms of the public realm, no element is more important than streets. This is where active travel to work, shop, eat out, and engage in other daily activities takes place, and where walking for exercise mostly occurs. Parks, plazas, trails, and other public places also have an important role in physical activity, but given the critical role and ubiquity of streets, this book focuses on the qualities that make one street more inviting and walkable than another. Think of your last trip to a great European city and what, other than the historic structures and the food, was memorable. You walked its streets for hours and did not tire. It is the magic of a great street environment.

Until recently, the measures used to characterize the built environment have been mostly gross qualities such as neighborhood density and street connectivity (see reviews by Ewing and Cervero 2010; Handy 2005; and Ewing 2005). The urban design literature points to subtler qualities that may influence choices about active travel and active leisure time. Referred to as perceptual qualities of the urban environment, or urban design qualities, such qualities are presumed to intervene between physical features and behavior, encouraging people to walk (see figure 1.1). Testing this presumption requires reliable methods of measuring urban design qualities, allowing comparison of these qualities to walking behavior.

Many tools for measuring the quality of the walking environment have emerged in the past few years. Generically called walking audit instruments, these are now used across the United States by researchers, local governments, and community groups. Robert Wood Johnson's Active Living Research (ALR) website alone hosts sixteen walking audit instruments. They involve the measurement of such physical features as building height, block length, and street and sidewalk width.

Urban design qualities are more than the individual physical features that they comprise, as they have a cumulative effect that is greater than the sum of the parts. Physical features individually may not tell us much about the experience of walking down a particular street. Specifically, they do not capture people's overall perceptions of the street environment, perceptions that may have complex or subtle relationships to physical features.

Perceptual qualities are also different from such qualities as sense of comfort, sense of safety, and level of interest, which reflect how an individual reacts to a place—how a person assesses the conditions there, given his or her own attitudes and preferences. Perceptions are just that—perceptions. They may elicit different reactions in different people. They can be assessed objectively by outside observers; individual reactions cannot.

Our challenge in creating a tool to measure urban design qualities was to move from highly subjective definitions to operational definitions that capture the essence of each quality and can be measured reliably across raters, including those without training in urban design.

Why You Should Read This Book

Measuring Urban Design provides operational definitions and measurement protocols for five intangible qualities of urban design: imageability, visual enclosure, human scale, transparency, and complexity. To help disseminate these measures, this book also provides a field survey instrument that has been tested and refined for use by lay observers.

This instrument has several strengths. First, it is grounded conceptually in constructs from architecture, urban design, and planning. Second, it has been carefully tested and validated. Third, it comes with detailed instructions for assessing the five urban design qualities. For these reasons, the instrument offers researchers a "gold standard" for the systematic measurement of urban design. A test in New York City showed that the instrument can be implemented in large-scale studies relating the built environment to social, psychological, and health outcomes.

Initial Screening of Qualities

Key perceptual qualities of the urban environment were identified based on a review of the classic urban design literature. Without much empirical evidence, these qualities are presumed to influence people's decisions to walk rather than drive to a destination, stroll in their leisure time, or just hang out and socialize on a street. Perceptual qualities figure prominently in such classics as those listed in box 1.1.

The research team also reviewed the visual preference and assessment literatures, which attempt to measure how individuals perceive their environments and to better understand what individuals value in their environments. Partial listing of this voluminous empirical literature is provided in Ewing (2000) and updated in Ewing et al. (2005). These literature reviews go beyond the boundaries of urban design to the fields of architecture, landscape architecture, park planning, and environmental psychology, as perceptual qualities of the environment figure prominently in these fields as well.

Our review yielded a list of fifty-one perceptual qualities of the urban environment (box 1.2). Of these fifty-one qualities, eight were selected for further study based on the importance assigned to them in the literature: imageability, enclosure, human scale, transparency, complexity, coherence, legibility, and linkage. Of the eight, the first five were successfully measured in a manner that passed tests of validity and reliability.

Imageability

Imageability is the quality of a place that makes it distinct, recognizable, and memorable. A place has high imageability when specific physical elements and their arrangement capture attention, evoke feelings, and create a lasting impression. It is probably not one element by itself that makes a street imageable but rather the combination of many.

According to Kevin Lynch (1960), a highly imageable city is well formed, contains distinct parts, and is instantly recognizable to anyone who has visited or lived there. It plays to the innate human ability to see and remember patterns. It is a city whose elements are easily identifiable and grouped into an overall pattern.

Landmarks are a component of imageability. The term landmark does not necessarily denote a grandiose civic structure or even a large object. In the words of Lynch, it can be "a doorknob or a dome." What is essential is its singularity and location, in relationship to its context and the city at large. Landmarks are a principle of urban design because they act as visual termination points, orientation points, and points of contrast in an urban setting. Tunnard and Pushkarev (1963, p. 140) attribute even greater importance to landmarks, saying, "A...