R ggmap: Why can I create rectangular maps using the filename attribute, but not use them in a plot?

Question

I would like to create a world map in R. I'm somewhat familiar with ggmap, so I tried something like this:

ggmap(get_googlemap(center=c(83,25),
                    zoom=1, scale=4, filename="world", size=c(640,300)))

It does work fine as far as the world.png is concerned.

I was actually quite happy to have found a workaround for ggmap's "can't show anything above 80° latitude" issue, due to which it's more or less impossible to create maps of the whole world.

However, in R itself, that is in the plots, the map looks not at all the way it's supposed to:

This only happens when the map is rectangular (when the size attribute is set accordingly), and not square (as would be the default).

Why's that? Is there any chance that this issue will be resolved in the future? And what's the quickest way from here to a proper world map?

Strake

Why not just save the .png then load it as a background image in ggplot? – Haemin

Would you mind giving me a hint as to how that would work? I know that it's possible to load a background image in ggplot, but I haven't been able to find a working solution in which the lon/lat ticks are aligned properly. – Strake

From ?ggmap, "maps of the whole world currently not supported". – Illdisposed

@AndyClifton: Sorry if I wasn't clear enough: I'm aware of that. The main reason I asked the question was that I'm trying to find a workaround for this problem. – Strake

Answer 1

Use a scale limit.

Normal map

ggmap(get_map(location=c(28.978359,41.008240), zoom=13, scale="auto"))

Rectangular (cropped) map

ggmap(get_map(location=c(28.978359,41.008240), zoom=13, scale="auto")) +
    scale_x_continuous(limits = c(28.925,29.025), expand = c(0, 0)) +
    scale_y_continuous(limits = c(40.99,41.03), expand = c(0, 0))

Glassware