R help - Sep 2006 - Question about span in Loess function

Hi,
 
I want to do 2-dimentional loess smoothing in gam through the command
 
gam(Y~lo(X1,X2,span=span,degree=1) )
 
in library "gam".
 
The span is the percentage of data points to define the neighborhood and used
for the smoothing.
 
Does this command do one 2-dimentional smoothing with neighboring defined
according to the radius of the data point || X=(X1,X2) ||, or it does two
1-dimentional smoothing which smooths X1, X2 separately?
 
I'm actually doing spatial smoothing with longitude and latitude, so I need
the 2-dimentional smoothing so the results won't depend on the coordinate
values.
 
Thanks a lot!!!
 
Best,
Yijie Zhou

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