80 research outputs found
The nested structure of urban business clusters
Although the cluster theory literature is bountiful in economics and regional
science, there is still a lack of understanding of how the geographical scales
of analysis (neighbourhood, city, region) relate to one another and impact the
observed phenomenon, and to which extent the clusters are industrially bound or
geographically consistent. In this paper, we cluster spatial economic
activities through a multi-scalar approach following percolation theory. We
consider both the industrial similarity and the geographical proximity of
firms, through their joint probability function which is constructed as a
copula. This gives rise to an emergent nested hierarchy of geoindustrial
clusters, which enables us to analyse the relationships between the different
scales, and specific industrial sectors. Using longitudinal business microdata
from the Office for National Statistics, we look at the evolution of clusters
which spans from very local groups of businesses to the metropolitan level, in
2007 and in 2014, so that the changes stemming from the financial crisis can be
observed.Comment: 20 pages, 10 figure
Paradoxical Interpretations of Urban Scaling Laws
Scaling laws are powerful summaries of the variations of urban attributes
with city size. However, the validity of their universal meaning for cities is
hampered by the observation that different scaling regimes can be encountered
for the same territory, time and attribute, depending on the criteria used to
delineate cities. The aim of this paper is to present new insights concerning
this variation, coupled with a sensitivity analysis of urban scaling in France,
for several socio-economic and infrastructural attributes from data collected
exhaustively at the local level. The sensitivity analysis considers different
aggregations of local units for which data are given by the Population Census.
We produce a large variety of definitions of cities (approximatively 5000) by
aggregating local Census units corresponding to the systematic combination of
three definitional criteria: density, commuting flows and population cutoffs.
We then measure the magnitude of scaling estimations and their sensitivity to
city definitions for several urban indicators, showing for example that simple
population cutoffs impact dramatically on the results obtained for a given
system and attribute. Variations are interpreted with respect to the meaning of
the attributes (socio-economic descriptors as well as infrastructure) and the
urban definitions used (understood as the combination of the three criteria).
Because of the Modifiable Areal Unit Problem and of the heterogeneous
morphologies and social landscapes in the cities internal space, scaling
estimations are subject to large variations, distorting many of the conclusions
on which generative models are based. We conclude that examining scaling
variations might be an opportunity to understand better the inner composition
of cities with regard to their size, i.e. to link the scales of the city-system
with the system of cities
Uncovering structural diversity in commuting networks: global and local entropy
In this paper we revisit the concept of mobility entropy. Over time, the structure of spatial interactions among urban centres tends to become more complex and evolves from centralised models to more scattered origin and destination patterns. Entropy measures can be used to explore this complexity, and to quantify the degree of structural diversity of in- and out-flows at different scales and across the system. We use toy models of commuting networks to examine global and local measures, allowing the comparison to occur between different parts of the system. We show that entropy at the link and node level give different insights on the characteristics of the systems, enabling us to identify employment hubs and interdependencies between and within different parts of the system. We compute the measures in the commuting networks of the Northern Powerhouse and Greater South East regions in the UK to examine their relevance when studying real systems of cities. Finally we discuss how these can be used to inform planning and policy decisions oriented towards decentralisation and resilience
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