Working with shapefiles, projections and world maps in ggplot
In this post I will show some different examples of how to work with map
projections and how to plot the maps using ggplot. Many maps that are
shown using their default projection are in the longlat-format, which is
far from optimal. For plotting world maps I prefer to use either
Robinson or Winkel Tripel projection—but many more are available—and I
will show how to use both these projections.
Before we get started you need to download a couple of shapefiles that we will use. You can find them here:
- http://www.naturalearthdata.com/downloads/110m-physical-vectors/110m-land/
- http://www.naturalearthdata.com/downloads/110m-cultural-vectors/110m-admin-0-countries/
- http://www.naturalearthdata.com/downloads/110m-cultural-vectors/110m-populated-places/
- http://www.naturalearthdata.com/downloads/110m-physical-vectors/110m-graticules/
Put them directly inside your working directory. We will use functions
from the rgdal-package to read the shapefiles into R, so if you do not
have it, you need to install it before you continue.
This will create a longlat-projected world map.
Here the world map is shown using the Robinson
projection.
However, the Caspian sea is missing. This is because of how ggplot handles polygon holes. Ggplot will plot polygon holes as a separate polygon, thus we need to make it pseudo-transparent by changing its fill color.
![World map in ggplot2 polygon hole example][./img/map3.png]
Now the Caspian sea is visible.
If we want we can also add a graticule and a bounding box. The bounding box is useful if we want to make the sea blue—especially when using some form of curved projection. Here I have added a graticule and bounding box to the longlat-map.
Robinson projection with added graticule and bounding
box.
Here I have added country borders to the previous map
plot.
Bubble plots are a popular way of displaying information on
maps. Here I used project() to reproject the bubbles’ coordinates into
the Robinson projection.
Lastly, here is an example of the Winkel tripel projection. This
projection became popular after 1998 when the National Geographic
Society choose to use it for their world maps—using it to replace the
Robinson projection, which they previously used.
Written by Kristoffer Magnusson, a researcher in clinical psychology. You should follow him on Twitter and come hang out on the open science discord Git Gud Science.
Published May 23, 2013 (View on GitHub)
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Archived Comments (13)
Tack, det här är jättebra. Jag måste dock tweaka lite pga vill inte ha default centrering, så det blir lite krångliare. Jag har hellre en brytning i atlanten än i Stilla Havet, så dom flesta lösningar jag hittar för bra projektioner måste jag modda mer.. men.. jaja. Tack i alla fall ^^!
Great Tutorial. Thanks Kristoffer. I do have a problem with the projection when I get the map data from maps library:
map <- map_data("world")
map <- subset(map, region!="Antarctica")
map <- spTransform(map, CRS("+proj=wintri"))
Gives me this error:
Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function ‘spTransform’ for signature ‘"data.frame", "CRS"’
Any clue of why this might be?
Thanks.
could you guys please help me out with my query.............I would like to create a calender using (R- studio) and i want to show the description pop-up on the date field when i moves my courser on a
specified date.
wanting to learn how to use shape files within R, tried replicating your tutorial. Using latest ver of required libraries and shape files. Now getting err: - Error in ogrInfo(dsn = dsn, layer = layer, encoding = encoding, use_iconv = use_iconv, : Cannot open file. Online references point to 'possible errs in topography'. I notice that your tutorial on R-bloggers now displays the map graphics as broken links. Any thoughts?
I tried but didn't succeed (sorry, just started with R), how may I change the colours of the countries, e.g. fill the United States with blue and Japan with yellow? Is there an easy way to do that?
I think readOGR/rgdal changed somehow (and I have the latest version), it only worked when I read it in as wmap <- readOGR(dsn="path to the folder which contains the shapefiles", layer="ne_110m_land").
Amazing tutorial!!
Short update: I managed to project my own data onto the map, however I failed in converting my long-lat data to robinson projection. Have to use the normal projection instead.
Hi, great post!! Is there a simple way to create a custom file with places instead of the one that you used. I have data from different places with long-and latt data, which I would love to project on that map.
Greetings
Friso
Thank you for the great and elegant post! Is there a simple way to add a specific latitude to the map? grat gives only a choice of major latitudes. What if I only want to draw a single latitude (and no longitudes) on the map?
Thanks for this. Nice post. Pretty new to the idea of mapping in R, surprised that there were so few tutorials around on the web. I was working on pulling the country names in too so you could tag a lists of countries for coding appropriately etc. Will look to post that back here once I have it refined. Cheers
This is great. Very easy to follow and expand upon. Actually, I was trying to grab the ocean shapefiles as well (I know it seems strange to overlay the ocean shapes onto the land shapefiles, but for I am doing it makes sense) and the website says that the "polygons are split into contiguous pieces." When I plot this downloaded files, it seems that it only shows the oceans around Asia and Africa. Not sure if that is supposed to be that way or I have something wrong. In the latter instance, using the routine described above does anyone know of a way to join these pieces together?
Nice post. I know the Robinson and Winkel projections work better overall, but being a Kiwi I prefer the old fashioned Mercator projection if only because the others tend to turn New Zealand into a disortorted smear at the edge of the world...
Well, the Mercator projection will make Sweden look bigger than it is, so I'm not wholly against it. Luckily Sweden is close to the prime median, else it would probably look like New Zealand...