Nahoum Cohen. Urban Conservation. Cambridge, Mass.: M.I.T. Press, 1999. 359 pp. $52.95 (paper), ISBN 978-0-262-53161-0.
Reviewed by Michael Holleran (College of Architecture & Planning, University of Colorado, Denver)
Published on H-Urban (April, 2001)
Nahoum Cohen, an architect and town planner in Tel Aviv, sets out to describe "the emerging discipline of urban conservation," which is more-or-less historic preservation at an urban scale. Most of the book lays out a framework for analyzing city form. The last section discusses conservation in practice, and the book concludes with case studies in Europe, North America, and Israel.
Jonathan Barnett has described urban design as "designing cities without designing buildings." Urban conservation, then, must mean preserving cities without preserving buildings. That is, in historic parts of cities, making sure that even when buildings change, we preserve what is valuable in urban form. The subject is ambitious, worthwhile, and timely. Historic preservation has become a widespread part of our treatment of the built environment, and it is important to integrate it into the mainstream of planning and urban design. Unfortunately Urban Conservation does not deliver on this promise.
The first sections of the book lay out a system for classifying the elements of historic urban environments that might be worth conserving. It emphasizes street networks, land parcelization, and building heights. These are indeed important, though they hardly constitute "an entirely new way of looking at the city." (p. 133) Cohen's perspective is that of urban morphology, which has a long literature, though he does not refer to it. As morphologies go, his approach is almost purely formal. Cities unfold like crystals under a microscope, with little historical explanation of how and why people make these changes. Nor do people appear at the architectural scale - urban spaces are abstract geometry, never described in terms of our experience inhabiting or moving through them.
Much of Cohen's discussion of urban morphology revolves around the urban "web." He presents this as a term to be used for systematic analysis, but its definition remains elusive. The web refers to the pattern of streets and public spaces, but its scale shifts throughout the book; sometimes it is the metropolitan-scale framework of arterials that outline districts, and sometimes an architectural scale of a few blocks with their land parcels and buildings. Instead of an analytical tool we get a connoisseur's view of urban geometry: Bologna displays "a very pronounced and unifying city web which has its own repetitions, not always similar but very coherent, containing elements of urban cohesion in their system." (p. 150) Of Isfahan, in Iran, he finds that "there is every reason to call this type of web 'anarchic.'" (p. 149) The center of Florence has in a half-mile-wide area "a mixture of several grids or webs, patterns which affect each other, while it is still apparent, in its overall structure, that there is a strong affinity between the geometrical patterns used.? (p. 163)
Later Cohen turns his attention to design. One chapter, for example, addresses conservation of urban squares. Buildings may be replaced, he says, but the new structures must retain the dimensions and proportions of the space. In some cases dimensions will not be enough; materials or details may also be important. So far so good. Here we are at the heart of the subject, and we look for guidance on putting these principles into practice. Cohen illustrates twenty examples; only one (in Barcelona) appears to include a new building, and he does not discuss it. Examples of new design in old squares are not hard to find: in recent years the architectural press has featured the new wing of the National Gallery in London's Trafalgar Square and the Carre d'Art in Nimes, to name two. Almost every German city is a laboratory of rebuilt squares (Cohen shows Warsaw's Stare Miasto, a literal reconstruction after the war, and thus no real help on the question of fitting new into old). In fact probably most urban squares provide some material to illuminate this question, but all of Cohen's examples have adopted the traditional means of preserving the buildings around them, and thus all talk of conservation is hypothetical.
This is the problem with Urban Conservation: it remains almost always hypothetical. All around the world, architects, urban designers, planners and preservationists are grappling with these issues, sometimes well and sometimes badly, but none of these people, and none of their projects, appear in the book. If urban conservation is indeed an emerging profession, it would be helpful to see it in action and see that its conscious practice makes a difference.
By omitting human decisionmakers, the book avoids engaging any of the difficult and interesting decisions they must make. For example, Cohen like others notes how much cities are shaped by traditional lot sizes, which are widely threatened by changes in the technology and economics of development. So what are we to do? Do we insist upon buildings of traditional size, at the risk of great economic costs? Do we simulate traditional lots by varying facades or massing, at the risk of inauthenticity? He does not say.
The last sections of the book propose a methodology for urban conservation, but they start out in an odd direction. Cohen formulates an index of "conservation potential," in order to analyze which districts ought to be the focus of conservation efforts. But how often is that the question? In the real world we start out with a place that we believe to be of value, and the question is what to do with it. Cohen claims to address that question, with adjustments that show conservation potential rising in response to proposed actions, but he never explains how these adjustments are made. He never explains where any of the numbers come from.
They appear to be based mainly on formal analysis, taking as evidence only the shapes and relationships visible in the environment. Remarkably, Cohen is willing to perform these analyses solely on the basis of documentation by others - a classroom exercise from maps and photos. His case study of the Italian town of Capua is based on a 1972 book; his San Francisco case study is a recycling of Anne Vernez Moudon's 1986 Built for Change. 
He faults Alamo Square, the subject of Moudon's book, as a failure of urban conservation. This is an understatement, as parts of it were cleared in a 1960s Urban Renewal project (Cohen refers to his own goal as "urban renewal" apparently without realizing the phrase's unfortunate connotations in the United States). But why take as the book's only North American case study a forty-year-old project where "conscious conservation was not even attempted" (p. 327)?
While Cohen retroactively takes on modernist site planning, it is refreshing that he does appreciate the potential of architectural modernism as an historic environment. Kikar Magen David, a 1930s square in Tel Aviv, gets a higher rating for "conservation potential" than the book's Paris or Florence examples.
Urban Conservation includes hundreds of illustrations - maps, plans, drawings, photos, magnificent air photos. These are the book's strength. Captions contain more words than the text, and deliver more of the book's content. Many do not identify images by place or date (though labels can be a mixed blessing - two illustrations of Bern are identified as Basel, and Piazza Santa Croce in Florence is called "this central part of London?" (pp. 148, 291, 309). None of them are attributed as to source, which is both a surprise (many are clearly reproduced from elsewhere, and it seems unlikely that all are in the public domain) and a disappointment (some are wonderful illustrations and it would be nice to know where to find them).
Many of the photos are electronically manipulated, sometimes in subtle ways that may at first escape notice. In general, this bolsters their explanatory legibility, though some readers may find it annoying. Sometimes parts of photos are colored arbitrarily, or thrown into negative for no discernible reason (this is one book you can judge by its cover). Similarly, some of the maps have been colored either randomly or according to some key to which we are not privy. Some illustrations are enlarged far beyond the resolution of the original image.
At one point the author talks about these graphic manipulations: "By painting the public passages on the conservation plan a dark color, the web feature is emphasized and the result is a clearer picture of the urban area. Once the urban portrait is in plain view, the regularity of the emerging web comes into focus. This regularity can then be expressed in quantitative terms." (p. 133) He has not demonstrated that any of this can be quantified, but it is not clear that it matters. One good picture is worth a thousand numbers.
. Jonathan Barnett, Urban Design as Public Policy, (New York: Architectural Record, 1974), 29.
. Two examples are James E. Vance, Jr., The Continuing City: Urban Morphology in Western Civilization (Baltimore: Johns Hopkins University Press, 1990), or Spiro Kostof, The City Assembled: The Elements of Urban Form Through History (Boston: Little, Brown, 1992). See also Urban Morphology, the Journal of the International Seminar on Urban Form (Birmingham, England).
. Anne Vernez Moudon, Built for Change: Neighborhood Architecture in San Francisco (Cambridge, Mass.: M.I.T., 1986).
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