Urban Spatial Structure

The Poznań wedge-ring green system, developed by Czarnecki and Wodziczko, is one of the most permanent elements in the spatial structure of the city. However, the present development processes and investment pressure pose a serious threat to the stability of the system, while stipulations in binding planning documents, postulating its protection and enforcement, are superficial. In view of the contemporary concepts of the sustainable city, green infrastructure or ecosystem services, and the need to implement European legal solutions it is necessary to re-interpret the “classical” concept of the Poznań urban green system. This pertains both to its internal structures and ties with the supporting external ecosystems.

The aim of the paper is to analyze and compare the form and land use structure of Euro-Mediterranean cities by estimating spatial metrics and to present a way of using these metrics to examine whether there is a common typology of urban sprawl. Based on Urban Atlas data (2006), the land use composition in six large urban agglomerations (Madrid, Barcelona, Rome, Milan, Athens and Marseille) is analyzed, and the degree of low density development is identified. Certain modifications are applied to the original Urban Atlas data, and spatial metrics are estimated using the FRAGSTATS software. A methodology for evaluating urban sprawl patterns based on five types of spatial metrics, characterizing patch density, size/aggregation, shape, dispersion/contiguity, and mixing, is presented. Moreover, land use change dynamics in the period 2006-2012 are analyzed in order to identify the most recent trends in urban growth. Results are evaluated and a comparison between the cities is presented. The discussion tries to characterize the patterns of urban sprawl, recognizing that, although there are certain similarities, a common typology of urban sprawl is not evident. JEL Classification R110, R140

Metropolitan areas in the U.S. have become increasingly polycentric. Large employment subcenters have emerged outside of central cities, competing against the traditional city center for labor and businesses. The existing literature on land use and transportation focuses on passenger travel, providing little insight into the impact of polycentric metropolitan development patterns on freight activity. In this study, we use the Los Angeles region as a case study to examine the relationship between urban spatial development patterns and freight travel. Using the National Employment Time Series (NETS) data, we identify employment subcenters in metropolitan Los Angeles. We characterize freight activities associated with the subcenters using data from the Southern California Association of Governments (SCAG). We develop a regression model that estimates freight activity as a function of geographic characteristics, such as whether a location is in an employment subcenter, measures of nearby employment, access to the highway network, and proximity to intermodal freight facilities. The results indicate that employment is an important driver of freight activity; however, employment subcenters have an independent effect on freight activity. The results of this study suggest that further research on urban spatial structure and freight activity should assess the effects of employment subcenters and how their particular employment composition and characteristics are associated with freight activities at the metropolitan level. Such an approach would lead to more precise policy recommendations for urban goods movement.

Almost thirty years ago, United Nations
alerted about future human development
explaining the concept of sustainable
development. In the report “Our common
future”, known as Brundtland report, it is said:
„Humanity has the ability to make
development sustainable to ensure
that it meets the needs of the present
without compromising the ability
of future generations to meet their
own needs. The concept of sustainable
development does imply limits – not
absolute limits but limitations imposed
by the present state of technology and
social organization on environmental
resources and by the ability of the
biosphere to absorb the effects
of human activities. But technology
and social organization can be both
managed and improved to make way
for a new era of economic growth. The
Commission believes that widespread
poverty is no longer inevitable. Poverty is
not only an evil in itself, but sustainable
development requires meeting the basic
needs of all and extending to all the
opportunity to fulfill their aspirations
for a better life. A world in which
poverty is endemic will always be prone
to ecological and other catastrophes.”1
Limitations and social conditions of development
are ones of the main ideas of the concept
of sustainability. Even they have been presented
many years ago, they still prevails. During the
last years of XX Century, urban development
and sustainability were in discussion.
The advantages and disadvantages of two
models, the dispersed city and the compact city,
were in the center of the debate. Javier Monclús,
Francesco Indovina and other recognized town
planners and urban researchers pointed out the
main effects of a scattered urban development:
1. Dispersion of urban areas in the region;
2. Social and functional segregation;
3. High consume of resource land;
4. High consume of energy;
5. High emission of pollutants;
6. High cost of maintenance and operation.
Closer to present days, Bernardo Secchi,
another renowned urban planner, noted that
the challenges for city management are
sustainability, social inclusion and mobility.
And these are the questions that are present
in the research carried out during these
summer months. Therefore, this research
proposes to analyze three recent urban
developments in metropolitan areas (ryc. 2)
that correspond to three different contexts
of social and economic development.
The research tries to focus on sustainable urban
development. For this study, it is assumed
that sustainable urban development means:
4. an efficient use of resource land and of
energy;
5. the development of public transport;
6. an effective and a correct urban growth
management.
The three cases show three different ways
of answering the demands involving the
extension of the built-up areas. Some of them
are closer to a sustainable urban development,
other more distant, significantly further away.
And in all three cases we will find the articulation
(and the lack of articulation) between
political, design and technical definitions. In
all three cases, by action or omission, it is
put in value the need to program the growth
of the city in accordance with a project
and not only with generic urban regulations.
The analysis of the three cases allows us
to see what kind of city is being built and, also,
to draw some lessons that allow us to specify
what type of city we can / want to live in and build.