lisa.nc {ncf}R Documentation

Non-centered inidcators of spatial association

Description

lisa.nc is a function to estimate the (noncentred) local indicators of spatial association. The function requires multiple observations at each location. For single observations at each location use lisa

Usage

    lisa.nc(x, y, z, neigh, na.rm = FALSE, resamp=1000, latlon = FALSE, 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 a matrix of dimension n x p 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.
na.rm if TRUE, NA's will be dealt with through pairwise deletion of missing values.
quiet if TRUE the counter is supressed during execution.

Details

This is the function to estimate the (non-centered) local indicators of spatial association modified form Anselin (1995). 'correlation' is the average correlation within a neighborhood. The function requires multiple observations at each location.

Missing values are allowed – values are assumed missing at random.

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 correlation 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

lisa 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 <- cbind(
        rmvn.spa(x=x, y=y, p=2, method="exp"),
        rmvn.spa(x=x, y=y, p=2, method="exp")
        )

#lisa.nc analysis
    fit1 <- lisa.nc(x=x, y=y, z=z, neigh=3)
    ## Not run: plot.lisa(fit1)

[Package ncf version 1.1-3 Index]