[R-sig-Geo] Question about correcting for spatial autocorrelation

[Julie Lee-Yaw]

Hi 
I've posted this to the mixed models forum as well but thought people here might know:
I want to use the the correlation setting with corSpher in nlme to account for potential spatial autocorrelation in my data. My data include observations from across the globe with locations in latitude and longitude (decimal degrees). From the R help for corSpher, the syntax for their wheat example would be something like:
fm1Wheat2 <- gls(yield ~ variety - 1, corr =corSpher(c(28, 0.2), form = ~ latitude + longitude, nugget = TRUE))

My question is whether the latitude and longitude provided should be projected into a spatial projection that preserves distances or areas or whether providing decimal degrees is appropriate?
Many thanks!
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