library(maptools)
library(ggplot2)
library(RColorBrewer)

## set the working directory.

setwd("/xxx/xxx/")

## load the function we require later.

source("poly_coords_function.r")

## load the shapefile

sport<- readShapePoly("london_sport.shp")

##have a look at the attribute table headings

names(sport)

## SpatialPolygons are complex objects in R. Accessing their geometry isn't straightforward but needs to be done in order for ggplot2 to be able to handle them. ggplot2 contains the "fortify" function that does this for you but I have been having problems with it on 64bit installations and macs so I have written my own function for this tutorial. It is simple enough to use the fortify command (remember to sort the table by the order field, and check the field headings) and go to the mapping step. It requires an ID field in the SpatialPolygonsdataframe, we will rename the "ons_label" field for this.

names(sport)<- c("ID", "name", "Partic_Per", "Pop_2001")

sport_geom<- poly_coords(sport)

## have a look at the sport_geom object to see its contents

head(sport_geom)

##Make the map of % sports participation in London boroughs. We will use the plot function.

map<- qplot(PolyCoordsY, PolyCoordsX, data=sport_geom, group=Poly_Name , fill= Partic_Per, geom="polygon")

map

# The default colours are really nice but we may wish to produce the map in black and white:

map + scale_fill_gradient(low="white", high="black")

# Or use another colour scheme such as one recommended by Color Brewer or introduce more breaks in the data:

new_fill<- function(pal, lowerlim, upperlim){
scale_fill_gradientn(colours= pal, limits=c(lowerlim, upperlim))
}

# The function above requires the name of the colour palette and any parameters required for it as well as the upper and lower limits of the data you wish to plot. 

map+new_fill(brewer.pal(7, "Blues"), 0, 30)


## See rspatialtips.org.uk for more info.

##
##Disclaimer: The methods provided here may not be the best solutions, just the ones I happen to know about! No support is provided with these worksheets. I have tried to make them as self-explanatory as possible and will not be able to respond to specific requests for help. I do however welcome feedback on the tutorials. License: cc-by-nc-sa. Contact: james@spatialanalysis.co.uk