[R-sig-Geo] Choropleth map

[James Rooney]

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 [r-sig-geo-bounces at r-project.org] On Behalf Of Janka VANSCHOENWINKEL [janka.vanschoenwinkel at uhasselt.be]
Sent: 24 June 2014 18:35
To: 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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