lisa {ncf}R Documentation

Local inidcator of spatial association

Description

lisa is a function to estimate the local indicators of spatial association. The function assumes univariate data at each location. For multivariate data use lisa.nc

Usage

    lisa(x, y, z, neigh, resamp, latlon, quiet = FALSE)
    

Arguments

x vector of length n representing the x coordinates (or latitude; see latlon).
y vector of length n representing the y coordinates (or longitude).
z vector of n representing p (>1) observation at each location.
neigh neighborhood size.
resamp number of resamples under the NULL to generate p-values
latlon Not yet implemented: if TRUE, coordinates are latitude and longitude.
quiet if TRUE the counter is supressed during execution.

Details

This is the function to estimate the local indicators of spatial association modified form Anselin (1995). The statistic is the average autocorrelation within a neighborhood.

Value

An object of class "lisa" is returned, consisting of the following components:

n the number of pairs within each neighborhood.
dmean the actual mean of distance within each neighborhood.
correlation the mean autocorrelation within the neighborhood (neigh).
p the permutation two-sided p-value for each distance-class.
coord a list with the x and y coordinates.

Author(s)

Ottar N. Bjornstad onb1@psu.edu

References

Anselin, L. 1995. Local indicators of spatial association - LISA. Geographical Analysis 27:93-115.

See Also

plot.lisa

Examples

#first generate some sample data
    x <- expand.grid(1:20, 1:5)[,1]
    y <- expand.grid(1:20, 1:5)[,2]

#z data from an exponential random field
    z <- rmvn.spa(x=x, y=y, p=2, method="exp")
    
#lisa analysis
    fit1 <- lisa(x=x, y=y, z=z, neigh=3, resamp=100)
    ## Not run: plot.lisa(fit1)

[Package ncf version 1.1-3 Index]