[R-sig-Geo] Combining polygons from a SpatialPolygonsDataFrame object

[Rafael Wüest]

Hi Jesus

gUnaryUnion (or gUnionCascaded) from the rgeos package can do this.

Have a look at the examples in the function documentation ?gUnaryUnion

> library(maptools)
> nc1 <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1], proj4string=CRS("+proj=longlat +datum=NAD27"))
> ID <- cut(lps[,1], quantile(lps[,1]), include.lowest=TRUE)
> reg4 <- gUnaryUnion(nc1, ID) # requires GEOS version 3.3.0

and look at

plot(reg4,lwd=2)
plot(nc1,add=T,lty=3)

If you set id to your province ID, you should get what you are looking for.

HTH,
Rafael


On 14.06.2012, at 09:45, Alonso Nanclares, Jesús Alberto wrote:

> Dear list,
>  
> I have a Shapefile representing the censal sections of Spain, and my interest is creating a KML file with only 52 polygons representing the different provinces of Spain. I shall use readOGR, and my problem comes when I have a SpatialPolygonsDataFrame object in R and I want to merge in only one polygon all the censal sections of every province. I have an attribute with the province ID defined in the same object, so it would only be aggregating the censal sections with the same province ID, but still I don’t know how to do it.
>  
> I shall be grateful for any help. My kind regards,
>  
> Jesús Alberto Alonso Nanclares
> Consultor Junior
> Centro de Competencias Business Analytics
> 
> Avda de Bruselas, 35
> 28108 Alcobendas (Madrid)
> España
> 
> T +34 914 805 863
> jaalonson at indra.es
> www.indracompany.com
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> <image001.jpg>
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Rafael Wüest
Swiss Federal Research Institute WSL
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