Prettymapr: Tools for rapid, nice-looking maps in R

Dewey Dunnington April 1, 2017

Prettymapr automates the process of creating a scale bar and north arrow in any package that uses base graphics to plot in R, or provides parameters that help to draw scale bars and north arrows in other plotting environments. Bounding box tools help find and manipulate extents, and geocoding tools help plot locations on maps. Finally, there is a function to automate the process of setting margins, plotting the map, scale bar, and north arrow, and resetting graphic parameters upon completion.

Installation

The prettymapr package is available on CRAN, and can be installed using install.packages("prettymapr"). The manual is also available on the CRAN website

Bounding box tools

The concept of a bounding box is integral to the rosm and rcanvec packages (as well as some others), so there’s a few tools to create/manipulate them here. I can never remember the proper way to create a bounding box using sp::bbox(), so the makebbox(n, e, s, w) function is included to make this process a little easier (I can somehow always remember ‘never eat shredded wheat’ for the cardinal directions). The easiest way to get these numbers is from the Open Street Maps Export page.

library(prettymapr)
makebbox(50.1232, -122.9574, 50.1035, -123.0042)

##         min       max
## x -123.0042 -122.9574
## y   50.1035   50.1232

It is, of course, easier to search for bounding boxes by human-readable location (google maps style), although this requires some confidence in the internet to recognize your location (the default source is the Pickpoint API, although you can pass source="google" to use the Google Maps API, or source="dsk" to use the Data Science Toolkit).

searchbbox("alta lake, british columbia")

##          min        max
## x -123.00891 -122.96891
## y   50.08865   50.12865

If you pass a vector into searchbbox() it will return the bounding box that contains all of them.

searchbbox(c("halifax, ns", "moncton, nb", "wolfville, ns"))

##         min       max
## x -64.91537 -63.41513
## y  44.48912  46.17745

And, if you don’t care to modify the values yourself to zoom in or out, you can use zoombbox().

bb <- makebbox(50.1232, -122.9574, 50.1035, -123.0042)
zoombbox(bb, 0.8) # zooms out a tad

##          min        max
## x -123.01005 -122.95155
## y   50.10104   50.12566

Geocoding tools

Sometimes it’s nice to be able to put cities on maps without having to look up their latitude and longitude, which is where the geocode() function comes in handy. It should be noted that the ggmap package also has a geocode() function that is also quite good, although didn’t serve my purposes of calculating bounding boxes. If you do a lot of this, please get your own API key so not everybody is using up mine (Google doesn’t require one, although if you have an enterprise account you can pass a key just as you would for pickpoint).

results <- geocode(c("halifax, NS", "wolfville, NS", "moncton, NB"))
names(results) # several standard columns

##  [1] "query"     "source"    "status"    "rank"      "lon"      
##  [6] "lat"       "address"   "bbox_n"    "bbox_e"    "bbox_s"   
## [11] "bbox_w"    "n_results" "id"

results[c("query", "address", "lon", "lat")]

##           query                                            address
## 1   halifax, NS       Halifax, Halifax County, Nova Scotia, Canada
## 2 wolfville, NS       Wolfville, Kings County, Nova Scotia, Canada
## 3   moncton, NB Moncton, Westmorland County, New Brunswick, Canada
##         lon      lat
## 1 -63.57513 44.64912
## 2 -64.36449 45.09123
## 3 -64.79897 46.09733

Mapping tools

There’s also a few mapping tools in prettymapr, most notably the prettymap() function, which evaluates its first argument while setting the margins to 0 (which is probably what you want for plotting a map). It also automatically adds a scalebar (although you could do this yourslef using the addscalebar() function).

library(rosm)
prettymap(osm.plot(searchbbox("nova scotia")))

Any plotting code has to go within prettymap(), so if you need multiple lines you can enclose them in curly brackets ({}). There’s tons of options for prettymap() that let you customize the north arrow, scale bar etc., which you can find in the prettymapr manual.

cities <- geocode(c("halifax, NS", "wolfville, NS", "moncton, NB"))
prettymap({
  osm.plot(searchbbox("nova scotia"))
  osm.points(cities$lon, cities$lat, pch=18)
})

Any plotting code that uses base plotting can be used inside prettymap(), including rosm, rcanvec, OpenStreetMap, cartography, marmap, and others. If only a scale bar or north arrow are required, there are independent functions to add to existing code.

library(maptools)
data("wrld_simpl")
plot(wrld_simpl, xlim=c(-131, -52), ylim=c(10, 55))
addscalebar()
addnortharrow()

That’s it for now! More convenience functions on the way…