spsurvey (version 3.4)

spbalance: Calculate Spatial Balance Metrics for a Survey Design

Description

This function calculates spatial balance metrics for a survey design. Two options for calculation of spatial balance metrics are available: (1) use proportions obtained from the intersection of Dirichlet tesselation polygons for the sample points with the frame object and (2) use proportions obtained from a rectangular grid superimposed on the sample points and the frame object. In both cases the proportions are used to calculate the spatial balance metrics. Two metrics are calculated: (1) the Pielou evenness measure and (2) the chi-square statistic.

Usage

spbalance(spsample, spframe = NULL, tess_ind = TRUE, sbc_ind = FALSE, nrows = 5,
   dxdy = TRUE)

Arguments

spsample

an object of class SpatialDesign produced by either the grts or irs functions that contains survey design information and additional attribute (auxiliary) variables.

spframe

an sp package object of class SpatialPointsDataFrame, SpatialLinesDataFrame, or SpatialPolygonsDataFrame that contains the survey design frame. The default is NULL.

tess_ind

a logical variable indicating whether spatial balance metrics are calculated using proportions obtained from the intersection of Dirichlet tesselation polygons for the sample points with the frame object. TRUE means calculate the metrics. FALSE means do not calculate the metrics. The default is TRUE

sbc_ind

a logical variable indicating whether spatial balance metrics are calculated using proportions obtained from a rectangular grid superimposed on the sample points and the frame. TRUE means calculate the metrics. FALSE means do not calculate the metrics. The default is FALSE.

nrows

number of rows (and columns) for the grid of cells. The default is 5.

dxdy

indicator for equal x-coordinate and y-coordinate grid cell increments, where TRUE means the increments are equal and FALSE means the increments are not equal. The default is TRUE.

Value

A list containing the following components:

tess

results for spatial balance metrics using tesselation polygons.

sbc

results for spatial balance metrics using a rectangular grid.

If either the tess_ind or sbc_ind arguments are set to FALSE, the corresponding component in the list is set to NULL. If tess_ind equals TRUE, then the list named tess is a list containing the following components:

J_subp

Pielou evenness measure.

chi_sq

chi-square statistic.

extent

frame extent for each Dirichlet tesselation polygon.

prop

frame proportion for each Dirichlet tesselation polygon.

If sbc_ind equals TRUE, then the list named sbc is a list containing the following components:

J_subp

Pielou evenness measure.

chi_sq

chi-square statistic.

extent_f

frame extent for each rectangular grid cell.

prop_f

frame proportion for each rectangular grid cell.

extent_s

sample extent for each rectangular grid cell.

prop_s

sample proportion for each rectangular grid cell.

References

Olsen, A. R., T. M. Kincaid, and Q. Payton (2012). Spatially balanced survey designs for natural resources. In R. A. Gitzen, J. J. Millspaugh, A. B. Cooper, and D. S. Licht (Eds.), Design and Analysis of Long-term Ecological Monitoring Studies, pp. 126-150. Cambridge University Press.

Examples

# NOT RUN {
design <- list(Stratum1=list(panel=c(PanelOne=50), seltype="Equal", over=10),
   Stratum2=list(panel=c(PanelOne=50, PanelTwo=50), seltype="Unequal",
   caty.n=c(CatyOne=25, CatyTwo=25, CatyThree=25, CatyFour=25), over=75))
frame <- read.shp("shapefile")
samp <- grts(design=design, DesignID="Test.Site", type.frame="area",
   src.frame="shapefile", in.shape="shapefile", att.frame=frame@data,
   stratum="stratum", mdcaty="mdcaty", shapefile=TRUE,
   shapefilename="sample")
spbalance(samp, frame, sbc_ind = TRUE)
# }