I’ve been using R in my daily doings more and more and as a student in the geo-sciences making maps is pretty important. My first love is still GMT, but R is proving useful and this is just a brief note on how to make a very simple map using R and ggplot2.

Get the shapefile:

wget http://biogeo.ucdavis.edu/data/gadm2.8/shp/ZAF_adm_shp.zip
unzip ZAF_adm_shp.zip

Install these packages (I’m lazy, so I just use the wildcard)

sudo apt install r-base-core libgdal\* libproj\* libgeos\*

Open R and first do:

install.packages(
c("ggplot2", "rgdal","rgeos","maps","sp")
)

The needed packages should be installed. Load the libraries and read the shapefiles. In this case ZAF_adm1 is South-Africa’s provincial demarcations.

library(ggplot2)
library(rgdal)
library(rgeos)
theme_set(theme_classic(base_size=22))

#Define the basemap as basemap, where dsn == the directory where the shapefile
#is located

basemap <- map_data(readOGR(dsn="southafrica", layer="ZAF_adm1"))

#We can get some stats on the basemap to set our boundaries
#summary(basemap)
#      long            lat             group           order       
# Min.   :16.45   Min.   :-34.84   Min.   : 1.00   Min.   :     1  
# 1st Qu.:20.82   1st Qu.:-31.34   1st Qu.:10.00   1st Qu.: 90332  
# Median :27.00   Median :-29.93   Median :18.00   Median :180662  
# Mean   :25.51   Mean   :-29.54   Mean   :23.19   Mean   :180667  
# 3rd Qu.:29.48   3rd Qu.:-27.31   3rd Qu.:29.00   3rd Qu.:270994  
# Max.   :32.89   Max.   :-22.13   Max.   :55.00   Max.   :361342  
#    region           subregion        
# Length:361288      Length:361288     
# Class :character   Class :character  
# Mode  :character   Mode  :character  

plt <- ggplot() +
geom_path(data=basemap, aes(x=long, y=lat, group=group)) +
coord_map(ylim=c(-22,-35), xlim=c(16, 33)) +
ggtitle("South-Africa") +
ylab("Latitude") + xlab("Longitude")

#To see the map
plt

#To save the map
png("SA_Map", width = 5 * 500, height = 5 * 500, res = 300)
plt
dev.off()

And tada, a map of South-Africa gmtmap

To add points in the map you can do

plt <- plt +
annotate("text", x = 28.3, y=-25.5, label = "PTA") +
annotate("point", x = 28.2293, y=-25.7479, colour = "red", size = 2.5)

or if you have a file with a ton of lat/lon points

#Assuming they are in a csv file (NAME,LAT,LON)
df <- read.csv("cities.csv", sep=",", header=TRUE)

plt <- ggplot() +
geom_path(data=basemap, aes(x=long, y=lat, group=group)) +
geom_point(data=df, aes(x=LON, y=LAT)) +
coord_map(ylim=c(-22,-35), xlim=c(16, 33)) +
ggtitle("South-Africa") +
ylab("Latitude") + xlab("Longitude")