


Dude, You are going way over my head. I think I lost you in the first sentence. Since this is probably a common task that alot of people have to do, can you provide an example of doing this. That would really help. I have a map of western US (camapzip_temp) and I am clipping the California portion of that. The CA (camap_base) portion is just a single polygon. The US map has zip code polygons and data attributes (zip codes) are attached to this map. I know your time is valuable but when ever you have some free time can you proved the modifications that are necessary to the code below. I would really appreciate it. This might be a silly question but why does the gIntersection function not work in this case. Keep in mind I am really new at this. My original attempt is below, 

{
cz_zip <- gIntersects(camapzip_temp,camap_base, byid=TRUE) 
out <- lapply( which(cz_zip) , function(x){ gIntersection( camapzip_temp[x,] , camap_base ) } )
keep <- sapply(out, class)
out <- out[keep == "SpatialPolygons"]
czout <- SpatialPolygons( lapply( 1:length( out ) , function(i) { Pol <- slot(out[[i]], "polygons")[[1]];   slot(Pol, "ID") <- as.character(i)
                                                                   Pol}))
}





     

> Date: Fri, 22 Nov 2013 19:59:53 +0100
> From: Roger.Bivand@nhh.no
> To: rvaid@hotmail.com
> CC: berman.jesse@gmail.com; r-sig-geo@r-project.org
> Subject: Re: [R-sig-Geo] Clipping a Map
> 
> On Fri, 22 Nov 2013, Ravi Vaid wrote:
> 
> >
> > Jesse,
> >
> > The clipping of the larger map by a smaller region works perfectly, but the resulting map (the clipped version) has the data component of the SP object missing. I can't merge anything if the data component is not there. I have tried directly using the gintersection function to clip the map but that seems to fail (waited more than 2 hours for the program to run).
> > When I run the command: slotNames(czout) I should get an object of name "data" along with the other 4 components below
> > but I only get,
> > I get: [1] "polygons"    "plotOrder"   "bbox"        "proj4string"So, somehow the "data" object is getting lost. I am fairly new to GIS, I just found the code for clipping on the sig-geo list and tried it and it worked, but the "data" object is missing. I know how to merge data but I just can't figure out how to recover the "data" component of the SP object.
> 
> No, you get a SpatialPolygons object. Obviously, the intersection will be 
> some subset of your clipped input object, but the function cannot lknow or 
> guess what you want. Suppose that you had a variable in the data slot that 
> was a count of some phenomenon - we don't know what proportion of the 
> count to retain if only part of the geometry is returned. This is clearly 
> up to the user to decide. Use the row.names() of the input and output 
> objects to identify which are which - use the accessor method to retrieve 
> the string values
> 
> row.names(camapzip_temp)
> row.names(camap_base)
> 
> and
> 
> row.names(cz_zip)
> 
> which are catenated from the input object row.names.
> 
> Hope this clarifies,
> 
> Roger
> 
> PS. Never, ever, assign directly to the data slot - this almost always 
> creates havoc and confusion by sidestepping checking of row.name values. 
> It's a really great way of randomising your data by accident, but 
> otherwise has no good justification.
> 
> >
> > Ravi
> >
> >
> >> Date: Fri, 22 Nov 2013 08:36:52 -0800
> >> From: berman.jesse@gmail.com
> >> To: r-sig-geo@r-project.org
> >> Subject: Re: [R-sig-Geo] Clipping a Map
> >>
> >> Hi Ravi,
> >>
> >> After performing 'gIntersects' try merging this result to your dataframe,
> >> then select the TRUE values?
> >>
> >> Jesse
> >>
> >>  cz_zip <- gIntersects(camapzip_temp,camap_base, byid=TRUE)
> >> camap_base@data<-cbind(camap_base@data, czip)
> >> camap2<-camap_base[(camap_base@data[,/???/] %in% c("TRUE)),] # Insert your
> >> column number for czip in place of ???
> >>
> >> plot(camap2)
> >> head(camap2@data)
> >>
> >>
> >>
> >> -----
> >> --------------------------------------------------------
> >> Jesse D Berman, PhD
> >> Yale University
> >> School of Forestry and Environmental Studies
> >> Post-Doc Fellow
> >> --
> >> View this message in context: http://r-sig-geo.2731867.n2.nabble.com/Clipping-a-Map-tp7585156p7585162.html
> >> Sent from the R-sig-geo mailing list archive at Nabble.com.
> >>
> >> _______________________________________________
> >> R-sig-Geo mailing list
> >> R-sig-Geo@r-project.org
> >> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
> >
> >
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> >
> > _______________________________________________
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> > R-sig-Geo@r-project.org
> > https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >
> 
> -- 
> Roger Bivand
> Department of Economics, NHH Norwegian School of Economics,
> Helleveien 30, N-5045 Bergen, Norway.
> voice: +47 55 95 93 55; fax +47 55 95 95 43
> e-mail: Roger.Bivand@nhh.no
> 

 		 	   		  
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