Run example(rworldmap) without the fields package and it errors out when it calls:

mapHalfDegreeGridToCountries()

beause 'fields' is in 'suggests' rather than 'depends'.

I think my reading of that 'suggests' is for in the docs makes me think its really a depends.

Thanks Barry, you are quite right, now fixed in version 1.21 available on CRAN. Andy