[gradsusr] Mask out and undefined Question

[Dana Doubler]

Hi there,

We are preparing climatological maps of the frequency and 
characteristics of jet maxima from gridded data.  On these maps we would 
like to "mask out" area with high elevations (>2 km) and also "mask out" 
areas  were no jets were reported in our study period.  We do not want 
the "0" or "missing value" indicators to be considered in the GrADS 
interpolation process.  We are using the command "undef" to define a 
masking value.  Ideally, however, we would like to show on the 
climatological maps the areas that have been masked due to high 
elevation in one color and the areas that have been masked because of no 
jet occurrences in another color.  We haven't been able to figure out 
how to do this.  Is this possible in GrADS?  Thanks in advance for your 
help.

Dana