[GIS] Pie charts on GIS maps using R

I'm an R user and have been using libraries like gistools and rgdal. I notice that ArcGIS appears to have features to add pie charts onto the maps themselves. (For example, if I have a map of the US, I can add a pie chart to each state). However, a quick search of gistools and rgdal documentation does not show any function to add such features.

Is there any easy way to add pie charts onto maps in R?

Best Answer

There are several options depending on which R package you want to use. The following links should give you some insights into some of the possibilities available.

Using mapplots and specifically the add.pie function (see this worked example and map below)
Using the rworldmap package as described here
Using the plotGoogleMaps package - see example here

(Map Sourced from: http://www.molecularecologist.com/2012/09/making-maps-with-r/)

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[GIS] Converting data.frame with no lat-long info to raster using R

So I've created a file that reads into a data frame in the same way as yours:

> str(v2)
'data.frame':   360 obs. of  720 variables:

BUT data.frame isn't really the right thing here. Its really meant for record-oriented data, where each row is a record and each column is a potentially different variable for that record (eg each row is a person, the columns are name, age, height, etc).

So you really only need to scan the data in as one long vector and feed it to a raster.

Step 1, define an empty raster of the right size and shape (note I'm assuming the raster covers the whole world, so the limits are not the cell centres):

> m2=raster(nrow=360,ncol=720,xmn=-180,xmx=180,ymn=-90,ymx=90)

Step 2, read numeric values into the raster data slot:

> m2[]=scan("d.txt",what=1)
Read 259200 items

And give it a projection if needed:

> projection(m2)="+init=epsg:4326"
> plot(m2)

If you want to check that the resolution and the cell centres are as expected, use these functions:

> res(m2)
[1] 0.5 0.5
> xFromCol(m2,1:10)
 [1] -179.75 -179.25 -178.75 -178.25 -177.75 -177.25 -176.75 -176.25 -175.75
[10] -175.25
> yFromRow(m2,1:10)
 [1] 89.75 89.25 88.75 88.25 87.75 87.25 86.75 86.25 85.75 85.25

which shows the resolution is half a degree and the cell centres (or at least the first 10) are at those specified coordinates.

[GIS] Extracting data, not colors, from geotiffs in R

They are the values in the file. How they correspond to measurements is unknown, and would have to be specified in external metadata.

A GeoTIFF can easily store decimal numbers in bands, and you can get the range simply enough. Here I read in a 3 band raster using stack and check the first band:

> dd = stack("d.tif")
> range(values(dd)[,1])
[1]   0.0000 801.1061
>

If you have information that says how you map your band-1 values to measurements then you just have to operate on the raster values. For example, to scale values from 0 to max(d1) to 0 to 2*pi:

d1 = dd[[1]] # get first band
d1 = d1 * 2 * pi / max(values(d1))

If your TIFF is one byte per value, and you want to scale it to 1 to 20, for example:

d1 = 1 + d1 * (19/255)

should do it.

Best Answer

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[GIS] Converting data.frame with no lat-long info to raster using R

[GIS] Extracting data, not colors, from geotiffs in R

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