spsurvey (version 2.6)

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(sp.sample, shapefilename=NULL, tess.ind=TRUE, sbc.ind=FALSE, nrows=5,
   dxdy=TRUE)

Arguments

sp.sample

the sp package object of class "SpatialPointsDataFrame" created by the grts or irs functions).

shapefilename

name of the input shapefile. If shapefilename equal NULL, then the shapefile or shapefiles in the working directory are read. 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. FA

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 th

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. Otherwise, each component of the list is a lists that contains the following components:
• J_subp
  Pielou evenness measure.
• chi_sq
  chi-square statistic.
• extent
  frame extent for each Dirichlet tesselation polygon or rectangular grid cell.
• prop
  frame proportion for each Dirichlet tesselation polygon or 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

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))
attframe <- read.dbf("shapefile")
samp <- grts(design=design, DesignID="Test.Site", type.frame="area",
   src.frame="shapefile", in.shape="shapefile", att.frame=attframe,
   stratum="stratum", mdcaty="mdcaty", shapefile=TRUE,
   shapefilename="sample")
spbalance(samp, shapefilename="shapefile", sbc.ind=TRUE)