Read shape files into Spatial*DataFrame objects

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Description

The readShapeSpatial reads data from a shapefile into a Spatial*DataFrame object. The writeSpatialShape function writes data from a Spatial*DataFrame object to a shapefile. Note DBF file restrictions in write.dbf.

Usage

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readShapeSpatial(fn, proj4string=CRS(as.character(NA)), 
	verbose=FALSE, repair=FALSE, IDvar=NULL, force_ring=FALSE, 
	delete_null_obj=FALSE, retrieve_ABS_null=FALSE)
writeSpatialShape(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

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 internal values, permitting such files to be read.

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 (Polygons only)

force_ring

if TRUE, close unclosed input rings (Polygons only)

delete_null_obj

if TRUE, null geometries inserted by ABS will be removed together with their data.frame rows (Polygons and Lines)

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 (Polygons only)

x

a vector data Spatial*DataFrame 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 Spatial*DataFrame object of a class corresponding to the input shapefile

Author(s)

Roger Bivand

See Also

write.dbf

Examples

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library(maptools)
xx <- readShapeSpatial(system.file("shapes/sids.shp", package="maptools")[1],
 IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
summary(xx)
xxx <- xx[xx$SID74 < 2,]
tmpfl <- paste(tempdir(), "xxpoly", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))
xx <- readShapeSpatial(system.file("shapes/fylk-val.shp",
 package="maptools")[1], proj4string=CRS("+proj=utm +zone=33 +datum=WGS84"))
summary(xx)
xxx <- xx[xx$LENGTH > 30000,]
plot(xxx, col="red", add=TRUE)
tmpfl <- paste(tempdir(), "xxline", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))
xx <- readShapeSpatial(system.file("shapes/baltim.shp", package="maptools")[1])
summary(xx)
xxx <- xx[xx$PRICE < 40,]
tmpfl <- paste(tempdir(), "xxpts", sep="/")
writeSpatialShape(xxx, tmpfl)
getinfo.shape(paste(tmpfl, ".shp", sep=""))
unlink(paste(tmpfl, ".*", sep=""))

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