Spatial Flows

Keyword(s):  
1984 ◽  
Vol 16 (4) ◽  
pp. 529-543 ◽  
Author(s):  
A S Fotheringham

The misspecification of gravity spatial interaction models has recently been described by the author. The bias in parameter estimates that results from such misspecification appears to produce the ‘map pattern effect’ or ‘spatial structure bias’ in estimated distance-decay parameters. A further aspect of the misspecification bias in gravity parameter estimates is explored here. The severity of the bias is shown to vary in a predictable manner with variations in spatial structure. In particular, the bias is shown to be dependent upon the pattern of accessibility that exists within a spatial system. The relevant aspects of this pattern are discussed for intraurban and interurban (or interregional) flow matrices. It is shown that from an examination of the spatial structure of centres in a spatial system it is possible, a priori, to identify whether significant bias will arise in the calibration of a gravity model. Certain configurations of centres are shown theoretically to produce maximal bias. The author thus answers the question, “why do gravity parameter estimates appear to be biased in some systems but not in others?”


1987 ◽  
Vol 19 (9) ◽  
pp. 1153-1160 ◽  
Author(s):  
M J Baxter

Methods of assessing model fit for models of spatial flows frequently do not take account of spatial structure. A nonparametric test, based on the signs of the residuals from a fit, is presented for detecting patterns in the residuals. It can be thought of as a general test of misspecification that can allow for spatial structure effects. It is argued that the test is most usefully applied with a model-building approach to data analysis.


2013 ◽  
Vol 58 (1) ◽  
pp. 147-159 ◽  
Author(s):  
C. Maddox ◽  
J. Corcoran ◽  
Y. Liu

2014 ◽  
Vol 281 (1777) ◽  
pp. 20132094 ◽  
Author(s):  
Justin N. Marleau ◽  
Frédéric Guichard ◽  
Michel Loreau

The addition of spatial structure to ecological concepts and theories has spurred integration between sub-disciplines within ecology, including community and ecosystem ecology. However, the complexity of spatial models limits their implementation to idealized, regular landscapes. We present a model meta-ecosystem with finite and irregular spatial structure consisting of local nutrient–autotrophs–herbivores ecosystems connected through spatial flows of materials and organisms. We study the effect of spatial flows on stability and ecosystem functions, and provide simple metrics of connectivity that can predict these effects. Our results show that high rates of nutrient and herbivore movement can destabilize local ecosystem dynamics, leading to spatially heterogeneous equilibria or oscillations across the meta-ecosystem, with generally increased meta-ecosystem primary and secondary production. However, the onset and the spatial scale of these emergent dynamics depend heavily on the spatial structure of the meta-ecosystem and on the relative movement rate of the autotrophs. We show how this strong dependence on finite spatial structure eludes commonly used metrics of connectivity, but can be predicted by the eigenvalues and eigenvectors of the connectivity matrix that describe the spatial structure and scale. Our study indicates the need to consider finite-size ecosystems in meta-ecosystem theory.


2003 ◽  
Vol 12 (2-3) ◽  
pp. 293-314 ◽  
Author(s):  
Pamela Odih

Formidable changes are occurring in the organization of work, production and the labour process. The emerging world of flexibility, part-time contracts and ‘just-in-time labour’ has invoked systemic disruptions in the sequential ordering of time/space. Feminists have been less than sanguine in their resistance to the placeless, timeless logic of ‘just-in-time labour’. The flexible fragmented present of post-fordist production is variously argued to be in contradiction to the embodied social relations through which women ‘weave’ their own autobiographies. While sympathetic to the concept of ‘feminine time’, its application to the present labour market context requires intense inquisition and critical reflection. The modern episteme consisted of a constellation of discourses linked to narrative realism. This is to appreciate that basic to all forms of gendered subjectivity is a conscious subject living in time and capable of uniting the literal with the virtual, or linking one temporal order (the present) with others (the past and future). The ‘timeless times’ and dislocated ‘spatial flows’ of our current era threaten the ability of gendered subjects to form their identities into sustained narratives. Focusing on post-fordist flexible specialization, this article challenges the fixed, unitary, relational subject of feminist critique and begins to deconstruct the problematics of gender and work in the time/space economy of ‘just-in-time’ labour.


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