[R-sig-Geo] How to overlay world map using non-standard projection

[Robert Hijmans]

>Problem is that I've been unable to overlay a map of the world. I've tried
to use the map() function, and >I've generated the map I want (right
projection and centered correctly) with the call: 

>library(maps) 
>world <-map(projection = "cylequalarea", parameter=30, interior=FALSE,
wrap=TRUE, ylim=c(->60,60),xlim=c(-180,180), orientation=c(90,-205,0)) 

>But when I try to overlay this map on the plot of my transformed
SpatialGrid I find that the scale of both >maps is completely different.
Their coordinates don't match: 

Perhaps you need to provide more parameters to map() (ellipsoid, datum?), as
it appears that it now uses something equivalent to an ellipsoid with radii
of about ~1 meter 

Robert
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