Offline Maps with RgoogleMaps and leaflets

M Loecher


New version of RgoogleMaps now fetches map tiles

Until version 1.3.0 RgoogleMaps only downloaded static maps as provided by the static maps APIs from e.g. Google, bing and OSM. While there are numerous advantages to this strategy such as full access to the extensive feature list provided by those APIs, the limitations are also clear:

  1. unlikely reusability of previously stored static maps,
  2. limits on the maximum size of the map (640,640),
  3. and the requirement to be online.

Beginning with version 1.4.1 (which is now on CRAN ) , we added the functions GetMapTiles and PlotOnMapTiles which fetch individual map tiles and store them locally.

For example, if we wanted to fetch 20 tiles (in each direction) at zoom level 16 around Washington Square Park in Manhattan, we would simply run

(center=getGeoCode("Washington Square Park;NY"))
##       lat       lon 
##  40.73082 -73.99733
GetMapTiles(center, zoom=16,nTiles = c(20,20))

Note that the default server is taken to be openstreetmap and the default local directory \(tileDir= "~/mapTiles/OSM/"\). We could have also passed the location string directly and saved several zoom levels at once (note the constant radius adaptation of the number of tiles):

for (zoom in 13:15)
  GetMapTiles("Washington Square Park;NY", zoom=zoom,nTiles = round(c(20,20)/(17-zoom)))

Before requesting new tiles, the function checks if that map tile exists already which avoids redundant downloads.

We can repeat the process with Google map tiles and plot them:

for (zoom in 13:16)
  GetMapTiles("Washington Square Park;NY", zoom=zoom,nTiles = round(c(20,20)/(17-zoom)),
              urlBase = "", tileDir= "~/mapTiles/Google/")

#just get 3x3 tiles:

#mt= GetMapTiles(center = c(lat = 40.73082, lon =-73.99733), zoom=16,nTiles = c(3,3), urlBase = "", tileDir= "~/mapTiles/Google/", returnTiles = TRUE)

mt= GetMapTiles("Washington Square Park;NY", zoom=16,nTiles = c(3,3),
              urlBase = "", tileDir= "~/mapTiles/Google/", returnTiles = TRUE)