Now passes devtools::check(). Should have tested before, sorry. Do you prefer one commit?

• Motivate the change in one paragraph, and include it in NEWS.
  In parentheses, reference your github user name and this issue:
  (@hadley, #1234)
• Check pull request only includes relevant changes.
• Use the official style.
• Update documentation and re-run roxygen2
• Add minimal example, if new graphical feature

BTW, this one is ready to be pulled I think.

Examples:
coord_map

coord_quickmap

If there is one thing left I'd like to change it would be the suppress the minor grid as in coord_map but I have no idea how to do this from within a coord function.

I wonder if it's worth noting that it's hard to see the difference between the two plots of NZ not because it's at a moderate latitude, but because the base file is already very detailed.

It might be worth plotting a rectangle bounding NZ to more clearly show the difference.

I'm not sure it's about the details, it's really about the latitude and the extent of the region.

Here is the code with a bounding box:

if (require("maps")) {
# Create a lat-long dataframe from the maps package
nz <- map_data("nz")
# Compute the bounding box
nz_bb <- nz[chull(nz[,c("long","lat")]),]
# Prepare a plot of the map
nzmap <- ggplot(nz, aes(x = long, y = lat)) +
  geom_polygon(data = nz_bb) + 
  geom_polygon(aes(group = group), fill = "white", colour = "black")

# Plot it in cartesian coordinates
nzmap
# With correct mercator projection
nzmap + coord_map()
# With the aspect ratio approximation
nzmap + coord_quickmap()

coord_map

coord_quickmap

I meant a rectangular bb so that you could see the difference. NZ might be a bad example but it'd be nice to have one

The difference is actually fairly small for anything under moderate latitudes. Even for the full US it's noticeable only for the northern states (that actually makes the functionality more appealing!). I guess it would show for northern canada or russia but this data is not in maps so it is difficult to make a self contained example.

Example:

Would that be better?

northern <- map_data("world")
northern <- northern[northern$lat > 50 & northern$lat < 80,]
northernmap <- ggplot(northern, aes(x = long, y = lat, group = group)) +
  geom_path()
northernmap + ggtitle("raw")
northernmap + coord_map() + ggtitle("coord_map")
northernmap + coord_quickmap() + ggtitle("coord_quickmap")

But coord_map has problems here...

Yeah, doesn't seem to be an easy way to generate a nice example, so lets not worry about it.

Great. Thanks for merging it! It'll be useful to be able to use this one for one class in which we produce a lot of tiled maps which coord_map made very long to plot and with (very thin but noticeable) white space showing between the tiles.

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