rworldmap颜色比例不连续

Question

I am using following example data and code to produce a map of world:

dF = read.table(text="
country, value
'France',  7
'United Kingdom',  64
'Italy',  68
'Sweden',  82
'Nepal',  85
'Japan',  86
'Germany',  86
'United States',  93
'China',  94
'Nigeria',  95"
, header=TRUE, sep=",")

library(rworldmap)

sPDF <- joinCountryData2Map(dF,
                            joinCode = "NAME",
                            nameJoinColumn = "country",
                            verbose = TRUE)

library(RColorBrewer)
colourPalette <- brewer.pal(7,'RdYlGn')
mapCountryData(sPDF,nameColumnToPlot="value",colourPalette=colourPalette)

However, the colors filled on map are not in a continuous scale. The United Kingdom is shown in almost the same color as France although their values are very different. Also China and United States are filled with different colors although their values are almost same. I think the colors are being filled as for categorical values and not on a continuous gradient scale. Changing the brewer.pal value from 7 to others does not help. How can I correct this? Thanks for your help.

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Edit

Adding dput of dF which will help others to reproduce data frame

structure(list(country = c("France", "United Kingdom", "Italy", 
"Sweden", "Nepal", "Japan", "Germany", "United States", "China", 
"Nigeria"), value = c(7L, 64L, 68L, 82L, 85L, 86L, 86L, 93L, 
94L, 95L)), .Names = c("country", "value"), class = "data.frame", row.names = c(NA, 
-10L))

Answer 1

Your issue is because you are using the default catMethod for mapCountryData which is 'quantiles'. If you set catMethod to 'fixedWidth' I think you will get a result closer to what you want.

mapCountryData(sPDF,nameColumnToPlot="value",colourPalette=colourPalette,catMethod='fixedWidth')

Or you can specify the category breaks with eg catMethod=c(0,20,40,60,80,100)

colourPalette <- brewer.pal(5,'RdYlGn')
mapCountryData(sPDF,nameColumnToPlot="value",colourPalette=colourPalette,catMethod=c(0,20,40,60,80,100))

Then you can add a more detailed legend if you wish.

mapParams <- mapCountryData(sPDF, nameColumnToPlot="value", colourPalette=colourPalette, catMethod=c(0,20,40,60,80,100), addLegend=FALSE)

do.call( addMapLegend, c( mapParams
                          , legendLabels="all"
                          , legendWidth=0.5 ))

Hope that helps.

Answer 2

Reason behind the plotting was, next value after France is UK plus you have 10 countries and you are dividing them into 7 categories which made France and UK in same color category. By default mapCountryData takes 7 category for plotting...

Following chart prepared by your code

Try to provide category exclusively. Try following...

colourPalette <- brewer.pal(nrow(dF),'RdYlGn')
mapCountryData(sPDF,nameColumnToPlot="value",colourPalette=colourPalette,numCats=nrow(dF))

Following chart prepared after introducing category exclusively

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Update

Case where you want only lower values to be colored red (in this case france)

library(fields)
colourPalette = two.colors(n=max(dF$value)-min(dF$value)+1, start="red", middle='yellow', end="dark green", alpha=1.0)
colourPalette = colourPalette[dF$value - min(dF$value) + 1]
mapCountryData(sPDF,nameColumnToPlot="value",colourPalette=colourPalette, numCats=nrow(dF))

Output would be