Maps in R

From r-bloggers

Start with the airports.

airports <- read.csv("airports.dat", header = FALSE)
colnames(airports) <- c("ID",
                    "name",
                        "city",
                        "country",
                        "IATA_FAA",
                        "ICAO",
                        "lat",
                        "lon",
                        "altitude",
                        "timezone",
                        "DST")
#head(airports)

Load in the routes for start/end.

routes <- read.csv("routes.dat", header=F)
colnames(routes) <- c("airline",
                    "airlineID",
                    "sourceAirport",
                    "sourceAirportID",
                    "destinationAirport",
                    "destinationAirportID",
                    "codeshare",
                    "stops",
                    "equipment")
#head(routes)

Basic map setup.

library(rworldmap)

## Loading required package: sp
## ### Welcome to rworldmap ###
## For a short introduction type :   vignette('rworldmap')

newmap <- getMap(resolution = "low")
plot(newmap, xlim = c(-20, 59), ylim = c(35, 71), asp = 1)
points(airports$lon, airports$lat, col = "red", cex = .6)

Start setup for a nicer map.

library(plyr)

Count number of departing from and arriving to airports.

departures <- ddply(routes, .(sourceAirportID), "nrow")
names(departures)[2] <- "flights"
arrivals <- ddply(routes, .(destinationAirportID), "nrow")
names(arrivals)[2] <- "flights"

Add meta on departing/arriving flights to airports dataset.

airportD <- merge(airports, departures, by.x = "ID", by.y = "sourceAirportID")
airportA <- merge(airports, arrivals, by.x = "ID", by.y = "destinationAirportID")

Load in google maps for a much prettier map

library(ggmap)

## Loading required package: ggplot2

map <- get_map(location = 'Europe', zoom = 4)

## Map from URL : http://maps.googleapis.com/maps/api/staticmap?center=Europe&zoom=4&size=640x640&scale=2&maptype=terrain&language=en-EN&sensor=false
## Information from URL : http://maps.googleapis.com/maps/api/geocode/json?address=Europe&sensor=false

# geom_point adds the data points layer kind of like ggplot would
# aes = aesthetics (points) are generated
mapPoints <- ggmap(map) +
    geom_point(aes(x = lon, y = lat, size = sqrt(flights)), data = airportD, alpha = .5)

mapPointsLegend <- mapPoints +
                   scale_size_area(breaks = sqrt(c(1, 5, 10, 50, 100, 500)),
                                   labels = c(1, 5, 10, 50, 100, 500),
                                   name = "departing routes")
mapPointsLegend

## Warning: Removed 2727 rows containing missing values (geom_point).

Faceting (couple of panels)

# create the data set containing both departures and arrivals
airportD$type <- "departures"
airportA$type <- "arrivals"
airportDA <- rbind(airportD, airportA)

# map the data
mapPointsDA <- ggmap(map) +
    geom_point(aes(x = lon, y = lat, size = sqrt(flights)), data = airportDA, alpha = .5)

# adjust the legend
mapPointsLegendDA <- mapPointsDA +
                     scale_size_area(breaks = sqrt(c(1, 5, 10, 50, 100, 500)),
                                     labels = c(1, 5, 10, 50, 100, 500),
                                     name = "routes")

# panels according to type (departure/arrival)
mapPointsFacetsDA <- mapPointsLegendDA + facet_grid(. ~ type)

mapPointsFacetsDA

## Warning: Removed 2731 rows containing missing values (geom_point).

## Warning: Removed 2727 rows containing missing values (geom_point).