Mapping SQL Relay locations using ggplot...

I may have planned to talk about too much in a one hour talk at SQL Relay. In terms of what I planned to show, I wanted to show a little bit of geomapping using ggplot.

Here is the visualisation of the SQL Relay locations drawn with ggplot:

This script illustrates a few interesting things about ggplot:

• you can plot polygons using the geom_polygon() function - complex shapes like maps
• you can use different data.frames for different 'layers' in a plot
• you can sequentially add extra detail to your visualisation - this script uses:
• geom_polygon()
• geom_point() - twice
• geom_text()
• ggtitle()

SCRIPT START

# draw a map of the UK with R. 

# https://www.students.ncl.ac.uk/keith.newman/r/maps-in-r

# install packages if necessary

library(maps)       # Provides functions that let us plot the maps

library(mapdata)    # Contains the hi-resolution maps.

library(ggmap)      # finds longitude and latitude values

library(ggplot2)    # high quality graphing

locs <- c("Nottingham England", "Reading England", "London England", "Bristol England", "Cardiff Wales", "Birmingham England")

locI <- c("N", "R", "L", "Br", "C", "Bi")

locCol <- c("darkgoldenrod1", "yellowgreen", "yellowgreen", "darkgoldenrod1", "blue", "tomato")

lonlat <- geocode(locs)

# draw a simple map of the United Kingdom

map('worldHires',

    c('UK'),

    xlim=c(-10,2), ylim=c(50,60))

# plot SQL Relay Locations info using base graphics

points(lonlat$lon,

       lonlat$lat,

       col= locCol,

       pch=19,

       cex = 1)

Map made with map() and base graphics

# we can also do this in ggplot better...

# make a data.frame 

data2 <- as.data.frame(locs)

# bind in longitude, latitude, colours and initials

data2 <- cbind(data2, lonlat, locCol, locI)

# use map_data() function to create a data.frame containing the map of the UK

uk<-map_data("worldHires", region = "UK")

# create the object m with the map using geom_polygon() function 

# we can make the map different colours

# see here for more about colours in R

# http://www.stat.columbia.edu/~tzheng/files/Rcolor.pdf

m <- ggplot() +

            geom_polygon(data=uk, 

                  aes(x=long, y=lat, group=group),

                  fill="gray88") +   # more about colours

            scale_x_continuous(limits = c(-10,3)) +

            scale_y_continuous(limits =c(49,60.9))

# add the points on the plot telling us where the longitude and latitude of various places

# N.B. the data is coming from a different data.frame to the map

# first add some black dots

m <- m +  geom_point(data=data2, 

                     aes(x=lon, y=lat), 

                     colour="black",

                     size = 7) 

# then some smaller coloured dots

m <- m +  geom_point(data=data2, 

                aes(x=lon, y=lat), 

                colour=locCol,

                size = 6)

  

# add the letters inside the circles  

m <- m + geom_text(data = data2, 

                   aes(x=lon, y=lat, label = locI, size = 4))

# change the theme to make the map nicer

m <- m + theme_bw()

# add a title

m <- m + ggtitle("SQL Relay Locations") +

         theme(legend.position="none") # get rid of the legend

m # show the object

Final map was exported as an A5 PDF which looked nice.

Resources:

• https://www.students.ncl.ac.uk/keith.newman/r/maps-in-r