Get Map with specified boundary coordinates
I want to get a map with RgoogleMaps from R, with a specific coordinates boundary.
What I can call is GetMap, and specify a center, I must add a zoom level. Everything works fine, except that I am not getting an image map bounded with the coordinates I choose.
Here's an example:
lat <- c(44.49,44.5) lon <- c(11.33,11.36) center = c(mean(lat), mean(lon)) zoom <- 14 mmap <- GetMap(center = center, zoom=zoom, maptype= "satellite", destfile = "m.png")
The problem is that only the center is passed as a parameter, and thus the whole image I see is dependant on the zoom level. So, I cannot really understand what are the boundaries of the image I get. What I want to do is to get an image bounded exactly with the coordinates I am defining. Is this possible (also with other map packages)?
Here is one way. First, you get a map with a certain zoom. Then, you add the lon and lat limit when you draw a figure, which you can do with scale_x_continuous and scale_y_continuous.
library(ggmap) library(ggplot2) ### Set a range lat <- c(44.49, 44.5) lon <- c(11.33, 11.36) ### Get a map map <- get_map(location = c(lon = mean(lon), lat = mean(lat)), zoom = 14, maptype = "satellite", source = "google") ### When you draw a figure, you limit lon and lat. foo <- ggmap(map)+ scale_x_continuous(limits = c(11.33, 11.36), expand = c(0, 0)) + scale_y_continuous(limits = c(44.49, 44.5), expand = c(0, 0)) foo
Another option is using OpenStreetMap as a source for your map. With the get_map function from the ggmap package, you can specify the boundaries of your map when you use OpenStreetMap as a source. With:
mmap <- get_map(location = c(11.33,44.49,11.36,44.50), source = "osm") ggmap(mmap)
However, this method does not work with GoogleMaps. Specifying the boundaries with GoogleMaps as a source will give you the following warning:
Warning: bounding box given to google - spatial extent only approximate. converting bounding box to center/zoom specification. (experimental)
A drawback of using OpenStreetMap is that you won't have access to satelite images.
Another way for an actual interactive Google Map is with my googleway package
library(googleway) lat <- c(44.49,44.5) lon <- c(11.33,11.36) zoom <- 14 mapKey <- 'your_api_key' google_map(location = c(mean(lat), mean(lon)), zoom = zoom, key = mapKey)
Which, being a Google Map, comes with satellite imagary as standard
I wish I had seen this question earlier. The RgoogleMaps package offers two ways of retrieving a map: GetMap(center, zoom) and GetMap.bbox(lonR,latR) which simply takes the bounding box as parameters. The zoom level is automatically computed. I think that the latter function could be what you are looking for. Markus