readShapePoly {maptools} | R Documentation

## Read polygon shape files into SpatialPolygonsDataFrame objects

### Description

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`.

### 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 internal values, permitting such files to be read.
`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

### Author(s)

Roger Bivand

### See Also

`write.dbf`

### 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=""))

[Package maptools version 0.8-39 Index]