[R-sig-Geo] Choropleth map

Edzer Pebesma edzer.pebesma at uni-muenster.de
Thu Jul 3 15:56:32 CEST 2014 

shape$IDs , as(shape, "data.frame"), as.data.frame(shape) should all work.


On 07/03/2014 02:34 PM, James Rooney wrote:
> Thank you Janka,
> 
> I'm aware of the solution and it is what I use myself. However Roger generally advises not to use @slots directly which is why I did not suggest the solution.
> 
> Roger I am curious is there an alternative here to using the @data construct with a match function ?
> 
> James
> 
> ________________________________________
> From: Janka VANSCHOENWINKEL [janka.vanschoenwinkel at uhasselt.be]
> Sent: 03 July 2014 09:35
> To: James Rooney; Roger.Bivand at nhh.no
> Cc: r-sig-geo at r-project.org
> Subject: Re: [R-sig-Geo] Choropleth map
> 
> Hi James and Roger,
> 
> You both pointed out that maybe I should not use the merge function to join data to an sp object.
> 
> I found the explanation for this on the internet (http://gis.stackexchange.com/) and thought it would be interesting to tell you:
> The merge function resorts the data during the operation which breaks the internal relationship in the sp object. Therefore to merge a dataframe to the @data slot of an sp object, using match is indeed better and is done in this way:
> 
> shape = name of shapefile
> Otherdata = data that I want to match
> IDS = identifier I want to merge on
> 
> shape at data = data.frame(shape at data, OtherData[match(shape at data$IDS, OtherData$IDS),])
> 
> 
> Furthermore, I have not yet entirely found the code to make the chloropleth plot, but I am getting there!
> 
> Thanks again for you advice,
> 
> Janka
> 
> 
> 
> 
> 
> 2014-06-25 14:40 GMT+02:00 James Rooney <ROONEYJ4 at tcd.ie<mailto:ROONEYJ4 at tcd.ie>>:
> Dear Janka,
> 
> I can't answer your ggplot questions as I don't really use it much however I did spot something in your code that will cause problems.
> 
> You used a "merge" to combine data between a dataframe and an SPDF:
> 
>> ValueMapDf <- merge(nuts, Value, by.x="NUTS_ID", by.y="NUTS_ID")
> 
> I've forgotten the reasoning, but this will not give you the merge results you expect. You might want to do some manual checking on your merge results.
> James
> 
> ________________________________________
> From: r-sig-geo-bounces at r-project.org<mailto:r-sig-geo-bounces at r-project.org> [r-sig-geo-bounces at r-project.org<mailto:r-sig-geo-bounces at r-project.org>] On Behalf Of Janka VANSCHOENWINKEL [janka.vanschoenwinkel at uhasselt.be<mailto:janka.vanschoenwinkel at uhasselt.be>]
> Sent: 24 June 2014 18:35
> To: r-sig-geo at r-project.org<mailto:r-sig-geo at r-project.org>
> Subject: [R-sig-Geo] Choropleth map
> 
> Dear list members,
> 
> 
> I am trying to make a basic choropleth map for all nuts3 regions in Europe
> ( = a map where
> 
> regions are colored by the value of a certain variable – think for instance
> about a populations
> 
>  density map).
> 
> 
> I am struggling with this for over a week by now and I always get the same
> error message:
> 
> Error: Aesthetics must either be length one, or the same length as
> 
>  the dataProblems:ValueMapDf$NUTS_ID
> 
> 
> 
> I checked the book “ggplot2” from Hadley Weckham and several internet
> sources.  They
> 
> document the different steps very properly, but still I don’t know what I
> am doing wrong.
> 
> 
> Could somebody help me out, please? Thanks in advance!
> 
> *Below you can find my code. I hope I gave sufficient information,
> otherwise, just let me know!*
> 
> 
> library(maptools)
> 
> library(ggplot2)
> 
> library(ggmap)
> 
> 
> # read administrative boundaries (I call the SpatialPolygonsDataFrame:
> "nuts" since it contains all nuts3 regions of Europe) )
> 
> nuts <- readShapePoly(fn="NUTS_RG_60M_2006")
> 
> names(nuts)
> 
> [1] "OBJECTID"   "NUTS_ID"    "STAT_LEVL_" "AREA"       "LEN"
> "Shape_Leng" "Shape_Area"
> 
> 
> # Then I have a dataset with over 60000 observations (several observations
> per nuts3 region). I take the average of the different
> 
> observations per nuts3 region and save it as "Value"
> 
> # The dataset is called Alldata and MEt is the variable I would like to map
> over the different nuts3 regions
> 
> 
> Value <- aggregate(Alldata$MEt,list(Alldata$nuts3),mean)
> 
> colnames(Value) <- c("NUTS_ID","ValueMEt")
> 
> 
> head(Value)
> 
>   NUTS_ID   ValueMEt
> 
> 1   AT111 0.04856170
> 
> 2   AT112 0.05448523
> 
> 3   AT113 0.04563415
> 
> 4   AT121 0.02164469
> 
> 5   AT122 0.02664611
> 
> 6   AT123 0.03163034
> 
> 
> 
> # merge map and data: I call the result "ValueMapDf"
> 
> ValueMapDf <- merge(nuts, Value, by.x="NUTS_ID", by.y="NUTS_ID")
> 
> ValueMapDf <- ValueMapDf[order(ValueMapDf$NUTS_ID),]
> 
> 
> 
> # then I dropped some regions of the SpatialPolygonsDataFrame, for which I
> don't have observations (I did this manually since I didn't
> 
> know if there was a way to do it automatically)
> 
> ValueMapDf<-ValueMapDf[ValueMapDf$OBJECTID > 441,]
> 
> ValueMapDf<-ValueMapDf[ValueMapDf$OBJECTID != 444,]
> 
> ValueMapDf<-ValueMapDf[ValueMapDf$OBJECTID != 447,]
> 
> ….
> 
> ValueMapDf<-ValueMapDf[ValueMapDf$OBJECTID != 1927,]
> 
> 
> 
> # So far so good: now I continue with plotting my map with the values!
> However, as you can see below, here something goes wrong.
> 
> # ggplot mapping
> 
> # data layer
> 
> m0 <- ggplot(data=ValueMapDf)
> 
> # fill with Value data
> 
> m1 <- m0 + geom_polygon(aes(x=long, y=lat, group=ValueMapDf$NUTS_ID,
> fill="ValueMapDf$ValueMEt")) + coord_equal()
> 
> # add map with only borders (to have visible borders)
> 
> m2 <- m1 + geom_path(aes(x=long, y=lat, group=ValueMapDf$NUTS_ID),
> color='black')
> 
> m2
> 
> Error: Aesthetics must either be length one, or the same length as the
> dataProblems:ValueMapDf$NUTS_ID
> 
> 
> 
> I also tried:
> 
> qplot(long,lat,data=ValueMapDf, group=ValueMapDf$NUTS_ID,
> fill=ValueMapDf$ValueMEt, geom="polygon")
> 
> Regions defined for each Polygons
> 
> Error: Aesthetics must either be length one, or the same length as the
> dataProblems:ValueMapDf$ValueMEt, ValueMapDf$NUTS_ID
> 
> 
> 
> 
> 
>> length(ValueMapDf$OBJECTID)
> 
> [1] 1122
> 
>> length(ValueMapDf)
> 
> [1] 1122
> 
>> length(ValueMapDf$NUTS_ID)
> 
> [1] 1122
> 
>> length(ValueMapDf$ValueMEt)
> 
> [1] 1122
> 
> 
> 
> *When I write:*
> 
> m0 <- ggplot(data=ValueMapDf)
> 
> # fill with Value data
> 
> m1 <- m0 + geom_polygon(aes(x=long, y=lat, group=NUTS_ID,
> fill="ValueMapDf$ValueMEt")) + coord_equal()
> 
> # add map with only borders (to have visible borders)
> 
> m2 <- m1 + geom_path(aes(x=long, y=lat, group=NUTS_ID), color='black')
> 
> m2
> 
> It get: Error in eval(expr, envir, enclos) : object 'NUTS_ID' not found
> 
> 
> 
>  Thanks in advance!
> 
> 
> Janka
> 
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> 
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> 

-- 
Edzer Pebesma
Institute for Geoinformatics (ifgi), University of Münster
Heisenbergstraße 2, 48149 Münster, Germany. Phone: +49 251
83 33081 http://ifgi.uni-muenster.de GPG key ID 0xAC227795

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