v.support response

[Dave Gerdes]

> > 
> > 
> > I have recently digitized landuse areas using v.digit.  On running v.support
> > I get the following error message:
> > 
> >     Warning:  area 141 label: 205 matched another label 205
> >     Warning:  area 143 label: 201 matched another label 205
> > 
> >        # of lines: 272
> >        # of nodes: 271
> >        # of areas: 272
> >        # of isles: 271
> >        # of atts: 402
> >        # of unattached atts: 0
> >        Snapped lines: 0
> > 
> > After running v.clean on the data, I still got the same warnings.  What does 
> > this mean and how do I fix the data.  There are many of these warning 
> > messages.
> > 
> > Thank you, 
> > Daphne

This is a common occurance after running v.patch, or r.poly.  It can also
happen through several different things while editing.

We start with the knowledge that area labels are attached by location in 
v.support.  The attribute X,Y will fall within one and only one area in 
the vector map.  And that is the area it will be attached to.  This
warning shows up whenever there are 2 or more area attributes which fall
inside the same area.   r.poly actually generates more than one correct label
for some areas and thus it is not uncommon to see these warnings on such
files.

In the case where the file was just edited, there are a number of scenarios
where this may happen.  Basically it tends to happen from an area being
editted (corrected) and re-labled without running v.support in between to
pick up the original label that got left out because of an error in the area.
Also if an area is built incorrectly by v.support this can happen.

To find and correct the problem above, you can use the area number (the 
first number listed) and under the debug menu '-' (this is documented in the
4.0 v.digit tutorial available on moon)   select the  'A - Find area' option
and then type in the number of the area of interest. This will highlight
that area, then you can check that area and the ones around it for any errors.
Generally that is enough to find the problem.  Use 'q' <CR> to exit
from this menu option.


As for making the warnings go away. That is what the mysterious question
below is for:

  Do you want to compress the Atts file? [n]

If you respond 'y' to this, it will overwrite the dig_att file with
exactly what is currently labelled in v.digit.  This prompt only comes
up if something has been editted in v.digit.  This command is like
v.clean except that it works on attributes instead of vectors.  Only 
use it when you are satisfied that your map is labelled correctly.


Hope that helped a little.

-- 



  Dave Gerdes
  US Army Construction Engineering Research Lab
  Spatial Analysis & Systems Team
  dpgerdes at zorro.cecer.army.mil
  (217) 352-6511 x591