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I downloaded some shapefiles from the Australian Bureau of Statistics (ABS). It's basically showing a bunch of suburbs when I view the shapefile through a GIS tool. The GIS tool that I am using at present is the GRASS 6.4.2 tool.

So basically the shapefile has the below statistics

Number of points:       0               Number of areas:      15231      
Number of lines:        0               Number of islands:    7003       
Number of boundaries:   31362           Number of faces:      0          
Number of centroids:    15220           Number of kernels:    0

I'm trying to extract from this shape file the arcs. That is the polylines of the boundaries. This is because I need to find for each arc its accompanying adjacent boundary.

For example arc1 may have boundary with Cat id - 135 on its left and Cat ID = 125 on its right.

Any clues as to how to do this would be appreciated.

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In GRASS the module v.to.db can "upload" the cat values of the right side and left side polygons into the boundary attribute table. From the v.to.db man page:

Upload category numbers of left and right area, to an attribute table of boundaries common for the areas:

   # add categories for boundaries of the input vector map, in layer 2:
   v.category soils out=mysoils layer=2 type=boundary option=add
   # add a table with columns named "left" and "right" to layer 2 of the input
   # vector map:
   v.db.addtable mysoils layer=2 col="left integer,right integer"
   # upload categories of left and right areas:
   v.to.db mysoils option=sides col=left,right layer=2
   # display the result:
   v.db.select mysoils layer=2

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