lisa function

Local indicator of spatial association

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

lisa(x, y, z, neigh, resamp = 999, 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: vector of n representing the observation at each location.
• neigh: neighborhood size.
• resamp: number of resamples under the NULL to generate p-values
• latlon: If TRUE, coordinates are latitude and longitude.
• quiet: If TRUE, the counter is suppressed during execution.

Returns

An object of class "lisa" is returned, consisting of the following components: - correlation: the autocorrelation within the neighborhood (neigh) of each observation measured using Moran's I.

• p: the permutation two-sided p-value for each observation.

• mean: the mean of the observations inside each neighborhooddistance within each neighborhood.

• n: the number of observations within each neighborhood.

• dmean: the actual mean distance within each neighborhood.

• z: the original observations

• coord: a list with the x and y coordinates.

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.

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 = "gaus")

# lisa analysis
fit1 <- lisa(x = x, y = y, z = z, neigh = 3, resamp = 499)
## Not run: plot(fit1, neigh.mean=FALSE)

References

Anselin, L. 1995. Local indicators of spatial association - LISA. Geographical Analysis 27:93-115. doi:10.1111/j.1538-4632.1995.tb00338.x

See Also

plot.lisa

Author(s)

Ottar N. Bjornstad onb1@psu.edu