ncf (version 1.1-2)

lisa: 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.

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.

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.

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)
    plot.lisa(fit1)