[R-sig-Geo] Plotting SpatialPolygonsDataFrame using ggplot2

[Paul Hiemstra]

Hi Hadley,

That worked like a charm. Thanks.

cheers,
Paul

hadley wickham wrote:
> Hi Paul,
>
> You're missing the group specification:
>
> ggplot(dum, aes(x = long, y = lat)) + geom_path(aes(group = group))
>
> Hadley
>
> On Tue, Apr 27, 2010 at 4:17 AM, Paul Hiemstra <p.hiemstra at geo.uu.nl> wrote:
>   
>> Hi people,
>>
>> I have a question regarding plotting a SpatialPolygonsDataFrame using
>> ggplot2. To convert the SPDF to a dataframe with the coordinates I already
>> use the excellent solution provided by Hadley in:
>>
>> http://tolstoy.newcastle.edu.au/R/e6/help/09/03/8668.html
>>
>> Some example code:
>>
>> library(maptools)
>> library(ggplot2)
>> x <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
>>     IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
>> dum = fortify(x, region = "CNTY_ID")
>> ggplot(dum, aes(x = long, y = lat)) + geom_path()
>>
>> My problem is that not only the counties are drawn, but also lines between
>> the end point of one countie polygon and the beginning of the next. I solve
>> this right now by adding the counties I want to plot one by one using:
>>
>> p + geom_path(subset(dum, id == 1) + geom_path(subset(dum, id == 2) + ...
>> etc
>>
>> This is of course a solution, but not an elegant one. Creating a new ggplot
>> object like:
>>
>> unique_ids = unique(dum$id)
>> bla = ggplot(subset(dum, id == unique_ids[1]), aes(x =long, y = lat)) +
>> geom_path()
>> for(id in unique_ids[2:length(unique_ids)]) {
>>      bla = bla + layer(data = subset(dum, id == id), mapping = aes(x =long,
>> y = lat), geom = "path")
>>   }
>> print(bla)
>>   Has exactly the same problem as using ggplot(dum, aes(x = long, y = lat))
>> + geom_path(). I browsed the net and the maling list and could not find the
>> answer, only references to the fortify() solution of Hadley.
>>
>> Anybody have an idea for an elegant solution to the problem?
>>
>> cheers,
>> Paul
>>
>> --
>> Drs. Paul Hiemstra
>> Department of Physical Geography
>> Faculty of Geosciences
>> University of Utrecht
>> Heidelberglaan 2
>> P.O. Box 80.115
>> 3508 TC Utrecht
>> Phone:  +3130 274 3113 Mon-Tue
>> Phone:  +3130 253 5773 Wed-Fri
>> http://intamap.geo.uu.nl/~paul
>> http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
>>
>> _______________________________________________
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>>
>>     
>
>
>
>   


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 274 3113 Mon-Tue
Phone:  +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul
http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770