proj4 support

[adeckmyn]

Having proj4 support in 'maps' would be useful. But it probably can only exist besides the old projection library, which for compatibility reasons can not be removed easily. So I will probably just add new options map(..., proj4="", proj4inv=FALSE)
The second allows for inverse projections of your data (which mapproj doesn't even implement)

[mdsumner]

You might use reproj which wraps `proj4' and handles the unit scaling

[adeckmyn]

Indeed. But my reason for closing the issue is that I decided taht, for now, there are already so many arguments to map() that adding more for proj4 is not very helpful. It is probably better to just call reproj (or proj4) separately with the output of map(). That is more or less what is happening anyway with packages that call map() for the basic lat/lon data only.

[mdsumner]

Sure, it should be that the plot device know its crs and modifies incoming data for it, that's how we wrap things 🙏