[R-sig-Geo] Choropleth map

[Roger Bivand]

Please do *not* post in HTML - all R lists require plain text.

You have not provided a reproducible example or access to downloadable 
data with a script showing your problem. Nobody will try to copy & paste 
from garbled HTML.

You are using ggplot, which mangles spatial objects. If the choropleth map 
can be created with plot or spplot methods from sp, you can go on to use 
ggplot, but you will most likely find it harder to debug all the way to 
ggplot without debugging the objects - so try spplot first.

Once that works, you are free to go on to ggplot. Have you looked at Oscar 
Perpigñán's book on displaying spatial data - your library should have it? 
Hadley Wickham's approach is to make all the fish into fish soup 
(fortify), from which it is hard to extract the fish for debugging. Debug 
the fish first before making your soup, especially checking dimensions.

Roger

On Tue, 24 Jun 2014, Janka VANSCHOENWINKEL wrote:

> 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
>
> 	[[alternative HTML version deleted]]
>
>

-- 
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no