segunda-feira, 18 de janeiro de 2021

Isard 1956: a estrutura urbana

ISARD W, Location and Space-Economy - A General Theory Relating to Industrial Location, Market Areas, Land Use, Trade, and Urban Structure. Cambridge, MA: MIT Press 1956.
http://www.economia.unam.mx/cedrus/descargas/locationspaceeco00isar%20(1).pdf



Texto clássico de economia espacial. Apesar do subtítulo A General Theory Relating to Industrial Location, Market Areas, Land Use, Trade, and Urban Structure, as generalizações do autor sobre a estrutura urbana têm de ser pacientemente garimpadas dentro do texto. As passagens que se seguem são dois exemplos. 

A estrutura urbana básica de Isard não difere em conteúdo das de HURD 1903 e BURGESS 1925. Como eles, Isard parte do princípio da expansão radial desigual a partir do centro, que é “dado” e tem a faculdade de se “desdobrar” a certa altura dos eixos radiais de expansão, formando a grande cidade policêntrica.

Burgess, que era sociólogo, intuindo talvez que o “centro” a partir do qual se dá a expansão periférica supõe a própria periferia, formulou em 1925, tendo em vista a Chicago metropolitana, o conceito de “descentralização centralizada”, que pode ser interpretado como: “na sociedade moderna, centro e periferia são as duas faces de uma mesma moeda” ou “na sociedade moderna, centro e periferia são reciprocamente determinados”.

Não sei se algum modelo econômico se propõe a dar conta dessa hipótese. Nos modelos econômicos monocêntricos de Wingo e Alonso, por exemplo, o centro já abriga todos os empregos e a renda / preço da terra decresce com a distância, conforme as ofertas da demanda.

A policentralidade de toda grande cidade não parece ser uma crítica relevante a esses modelos, como demonstra Isard: o centro principal se desdobra em subcentros e seus respectivos gradientes de preço / aluguel se interpenetram; aumenta a complexidade, multiplicam-se as singularidades (shopping centers, p. ex.), mas não muda o fundamento: o preço / aluguel decresce com a distância aos focos de interesse da demanda por localizações.

A questão que me parece pendente é: qual princípio, ou combinação de princípios, governa a ocorrência simultânea da distribuição radial-concêntrica das residências e do agrupamento central dos negócios? Serão, de fato, esses dois fenômenos reciprocamente determinados?

*

“(..) [The] spatial physiognomy of the urban-metropolitan region is a primary concern. Intensity of land use is a function of, among other factors, distance from the core. At the core the pyramiding of activities attains a maximum maximorum. With movement away along radials in all directions the intensity of land use diminishes, but differentially in the various directions. Moreover, the rate at which this intensity falls in any direction changes with distance. In addition, after a point along many of the radials, the intensity reaches a relative minimum, reverses its trend by creeping upward, and attains a relative maximum, only to decline again and perhaps to repeat this undulatory performance. Along a few of the radials, generally the strategic ones along which the rate of decline from the core is among the least for all radials, relative maxima for the entire metropolitan region are realized. These latter represent subfoci from which, for some distance at least, intensity falls off in all directions. The strategic radials also exercise a degree of dominance to the extent that, in directions perpendicular to their course, intensity decreases. 

In short, an urban-metropolitan region comes to comprise an hierarchy of strategic nodal sites, classifiable by order and degree of dominance. This multinucleated body is, viewed from another angle, a network of transport interconnections and hence of interstitial areas each subject to hierarchical order. (..)” [ISARD 1956 p. 11]

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“(..) The businessman interested in producing the commodity or service corresponding to use A also considers other sites as potential locations. Given the same set of values for advertising outlays, price mark-up, quality of product, and other relevant factors, he anticipates for each possible site a dollar volume of sales. (..) In general, it is to be expected that dollar volume of sales falls off with effective distance from the core although at times it rises to secondary peaks only to decline again. [39] (..)

[39] Where the urban structural pattern is set and relatively inflexible, these secondary peaks can be readily ascertained. They appear at those effective distances which separate secondary and satellite commercial and shopping centers from the core. In contrast, where the urban structural pattern is extremely fluid and largely to be determined, it is difficult to identify the effective distances from the core at which secondary peaks occur. Since secondary peaks reflect the juxtaposition of complementary activities and since in this latter setting the spatial configurations of all economic activities including transportation patterns are interdependent, only a general equilibrium (simultaneous equations) approach, which takes into account all aspects of complementarity and competition, yields the effective distances at which secondary peaks occur.” [ISARD 1956 p. 201]


2021-01-18