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. Note DBF file restrictions in write.dbf.

Keywords
spatial
Usage
readShapePoly(fn, IDvar=NULL, proj4string=CRS(as.character(NA)),
 verbose=FALSE, repair=FALSE, force_ring=FALSE, delete_null_obj=FALSE,
 retrieve_ABS_null=FALSE)
writePolyShape(x, fn, factor2char = TRUE, max_nchar=254)
Arguments
fn
shapefile layer name, when writing omitting the extensions *.shp, *.shx and *.dbf, which are added in the function
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
force_ring
if TRUE, close unclosed input rings
delete_null_obj
if TRUE, null geometries will be removed together with their data.frame rows
retrieve_ABS_null
default FALSE, if TRUE and delete_null_obj also TRUE, the function will return a data frame containing the data from any null geometries inserted by ABS
x
a SpatialPolygonsDataFrame object
factor2char
logical, default TRUE, convert factor columns to character
max_nchar
default 254, may be set to a higher limit and passed through to the DBF writer, please see Details in write.dbf
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 row.names are added to the DBF file as column SP_ID.

Value

  • a SpatialPolygonsDataFrame object

See Also

write.dbf

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(coordinates(xx), labels=row.names(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(), "xxpoly", 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 0.8-37, License: GPL (>= 2)

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