An Empirical Study of Price Correlations: 2. The Decrease in Price Correlation with Distance and the Concept of Correlation Length
The dependence of the correlation between wheat price fluctuations on different markets with respect to the distance between those markets is investigated. It is shown that the decrease in the correlation is exponential and is governed by a characteristic distance which is called the correlation length for wheat prices. This is a measure of the level of market integration in a given area. The magnitude of the correlation length is compared for different cereals: wheat, rye, and oats, and the evolution of the correlation length during the 19th century is studied. In particular, it is observed that subsistence crises are characterised by a collective behaviour of the economy which results in a sudden peak in the correlation length. Last, the part played by the spatial correlation between precipitations is investigated. It appears to be rather small; consequently, the price-correlation length is primarily the result of economic factors.
Map pattern and friction of distance parameters: a comment
This note maintains that a recent paper by Cliff, Martin and Ord is incorrect in its conclusions relevant to a paper by Johnston, as shown by data fitted to their hypothetical spatial system.
Explanation, Prediction, and Meaning Variance: An Assessment of Distance Interaction Models
The concept of spatial interaction is central for everyone concerned with theoretical geography and regional science. One reason may simply be that the term usually is defined so vaguely that it encompasses most forces which contribute to the birth, death, growth, and stability of spatial systems. Ullman [74] has in fact argued that the concept is even more general than that of areal differentiation, while Ackerman [1, p. 437] has related it more explicitly to the notions of connectivity and information flows. Similarly, Maruyama [42] and other general systems scientists have noted how interaction and information