A function to compute the distance-decay interaction index (DPxy)

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Description

The distance decay interaction index, DPxy, is a spatial adaptation of interaction index xPy. 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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DPxy(x, d = NULL, distin = 'm',  distout = 'm', diagval = '0', 
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

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)

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 numeric vector containing the distance-decay isolation index value for each population group

References

Morgan, B. S. (1983) An Alternate Approach to the Development of a Distance-Based Measure of Racial Segregation. American Journal of Sociology 88, pp. 1237-1249.

See Also

Isolation indices: xPx, Eta2, DPxx

Interaction index: xPy

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'

DPxy(x, d = dist)

DPxy(x, spatobj = segdata, diagval = 'a')

DPxy(x, folder = foldername, shape = shapename, diagval = '0') 

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