readShapePoly

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Read polygon shape files into SpatialPolygonsDataFrame objects

The readShapePoly reads data from a polygon shapefile into a SpatialPolygonsDataFrame object. The writePolyShape function writes data from a SpatialPolygonsDataFrame object to a shapefile.

Keywords
spatial
Usage
readShapePoly(fn, IDvar=NULL, proj4string=CRS(as.character(NA)), verbose=FALSE, repair=FALSE)
writePolyShape(x, fn, factor2char = TRUE)
Arguments
fn
shapefile layer name, without extension
IDvar
a character string: the name of a column in the shapefile DBF containing the ID values of the shapes - the values will be converted to a character vector
proj4string
Object of class CRS; holding a valid proj4 string
verbose
default TRUE - report type of shapefile and number of shapes
repair
default FALSE: some shapefiles provided by Geolytics Inc. have values of object sizes stored in the *.shx index file that are eight bytes too large, leading the function to try to read past the end of file. If repair=TRUE, an attempt is made to repair the
x
a SpatialPolygonsDataFrame object
factor2char
logical, default TRUE, convert factor columns to character
Details

If no IDvar argument is given, the shpID values of the shapefile will be used as Polygons ID values; when writing shapefiles, the object data slot rownames are added to the DBF file as column SP_ID.

Value

  • a SpatialPolygonsDataFrame object

Aliases
  • readShapePoly
  • writePolyShape
Examples
library(maptools)
xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
plot(xx, border="blue", axes=TRUE, las=1)
text(getSpPPolygonsLabptSlots(xx), labels=getSpPPolygonsIDSlots(xx), cex=0.6)
as(xx, "data.frame")[1:5, 1:6]
xxx <- xx[xx$SID74 < 2,]
plot(xxx, border="red", add=TRUE)
tmpfl <- paste(tempdir(), "xxline", sep="/")
writePolyShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
axx <- readShapePoly(tmpfl, proj4string=CRS("+proj=longlat +ellps=clrk66"))
plot(xxx, border="black", lwd=4)
plot(axx, border="yellow", lwd=1, add=TRUE)
unlink(paste(tmpfl, ".*", sep=""))
Documentation reproduced from package maptools, version 0.5-14, License: GPL version 2 or later (R and interface code), MIT (shapelib code)

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