[GRASSLIST:7221] Extract vector features from two (or more) maps?

[David Finlayson]

I am hoping someone can elaborate on this wiki post:

http://grass.gdf-hannover.de/twiki/bin/view/GRASS/GrassSixTutorialFaq

Q: How to extract from two layers and to make a selection at the same time? 

A: You have to create a third map layer (or add the spread attributes
to one layer) and upload the attributes from layer 1 and 2 to layer 3
(v.to.db option=query qcol=), then use v.extract on layer 3

A short example would be helpful. 

Also, from the help file for v.to.db what are layers and qlayers? 

Thanks,

David
-- 
David Finlayson
Marine Geology & Geophysics
School of Oceanography
Box 357940
University of Washington
Seattle, WA  98195-7940
USA

Office: Marine Sciences Building, Room 112
Phone: (206) 616-9407
Web: http://students.washington.edu/dfinlays