A function to compute the spatial proximity index (SP)

Description

The spatial proximity index, SP, compares the clustering level (mean proximity) of a group compared to another group. The function can be used in two ways: to provide a distance matrix or a external geographic information source (spatial object or shape file).

Usage

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SP(x, d = NULL, fdist = 'e', distin = 'm',  distout = 'm', diagval = '0', 
itype = 'multi', spatobj = NULL, folder = NULL, shape = NULL)

Arguments

x

- an object of class matrix (or which can be coerced to that class), where each column represents the distribution of a population group, within spatial units. The number of columns should be greater than 1 (at least 2 population groups are required). You should not include a column with total population in each unit, because this will be interpreted as a group.

d

- a matrix of the distances between spatial unit centroids

fdist

- the method used for distance interaction matrix: e' for inverse exponential function (by default) and 'l' for linear.

distin

- input metric conversion, based on bink package and includes conversions from 'm', 'km', 'inch', 'ft', 'yd', 'mi', 'naut_mi', etc.

distout

- output metric conversion, based on bink package and includes conversions to 'm', 'km', 'inch', 'ft', 'yd', 'mi', 'naut_mi', etc.

diagval

- when providing a spatial object or a shape file, the user has the choice of the spatial matrix diagonal definition: diagval = '0' (by default) for an null diagonal and diagval = 'a' to compute the diagonal as 0.6 * square root (spatial units area) (White, 1983)

itype

- a character string defining the index type: itype = 'multi' (by default) for the multigroup index (White, 1986) itype = 'between' for the between groups version (White, 1983) or itype = 'one' for the one-group version (Apparicio et al, 2008)

spatobj

- a spatial object (SpatialPolygonsDataFrame) containing geographic information

folder

- a character vector with the folder (directory) name indicating where the shapefile with the geographic information is located.

shape

- a character vector with the name of the shapefile (without the .shp extension) which contains the geographic information

Value

a matrix containing spatial proximity index values for each pair of groups

References

White M. J. (1983) The Measurement of Spatial Segregation. American Journal of Sociology, 88, p. 1008-1019.

White, M. J. (1986) Segregation and Diversity Measures in Population DistributionE. Population Index 52(2): 198-221.

Apparicio, P., V. Petkevitch and M. Charron (2008): Segregation Analyzer: A C#.Net application for calculating residential segregation indices, Cybergeo: European Journal of Geography, 414, 1-27.

See Also

Proximity measures: Pxx, Pxy, Poo

Clustering Indices: ACL, RCL

Examples

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x <- segdata@data[ ,1:2]
ar<-area(segdata)
dist <- distance(segdata)
diag(dist)<-sqrt(ar) * 0.6
foldername <- system.file('extdata', package = 'OasisR')
shapename <- 'segdata'

SP(x, spatobj = segdata)

SP(x, folder = foldername, shape = shapename, fdist = 'l', itype = 'between') 

SP(x, spatobj = segdata, diagval ='a', itype = 'one')

SP(x, d = dist, fdist = 'e')

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