ggmap, ggimage… - Saving and loading maps in R

Question

In my current R project I'm using the ggmap package to download and display maps. What bothers me is that you need internet access to load maps from google etc. I'd like to load a map from the internet and save it so I can work offline as well. An ideal solution should minimize the amount of code between get_map() (or a related command) and using the saved map within ggmap() (or a related command).

I know already that get_map() has a filename attribute to save maps as an image, and I also know the ggimage() method (I've never actually worked with it, though.) Is there a simple way save such a map, or are these two the best tools I have, and if so, how do you use them effectively?

Answer 1

Did you save the corresponding R object as well? E.g.:

# Download and save map image and R object
library(ggmap)
egy.map <- get_map(location=c(lon=30, lat=26), zoom=6, maptype="terrain", filename="~/Desktop/ggmapTemp")
save(egy.map, file="~/Desktop/egy-map.rda")

# Restart R or RStudio before running the code below
library(ggmap)
load("~/Desktop/egy-map.rda")
ls()
ggmap(egy.map)

This should let you download and save maps for later offline use, although maybe I misunderstood your question.