[gradsusr] How to Blank the contour outside some area via shape files

[zhaokuifeng]

Thanks for grads user mail list.
I have a question about draw map via shape files.
In the past,I use basemap to blank the contours outside my province.When I
use the SHP
files,I found 'draw shp' could not blank them except using 'basemap'.
Could anyone kindly  give me some advice on 'how to blank the contour
outside some area via shape files'?Thank you.
Best Regards.
         Zhao
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