cleaning up imported vector files

[Simon Cox]

I have a number of vector files which I am importing from other systems.
Unfortunately, in several of these the many of the polygon outlines have
been digitised twice - once for each of the polygons on either side of the
boundary.
This causes some problems with the topology, with areas not being closed,
sliver polygons, and the redundancy costs some performance etc.
I wonder if anyone has the right advice about how to clean this up.

I've tried running v.spag, but it goes for ever and doesn't finish.  I
think that
a problem is that although many of the lines are _almost_ coincident, they
are not quite, so I have the situation where spag is creating many many extra
nodes for the multiple intersections along approximately identical line
segments.
v.spag -i only finds a few truly identical lines.  I think I have to do
some snapping
and maybe some pruning as well as spag'ging in order to get a clean map,
but I'm
not sure of the optimal sequence.  I'm sure other people must have come across
this problem before, so I wonder if anyone has the right advice!

Please send a copy of replies to me directly as I'm having problems with my
grassu
subscription.

Thanks for your help                                    Simon Cox

_______________________________________________________
Dr Simon Cox - Australian Geodynamics Cooperative Research Centre
CSIRO Exploration & Mining,  PO Box 437,  Nedlands, WA 6009 Australia
T:  +61 9 284 8443    F:  +61 9 389 1906   simon at ned.dem.csiro.au
http://www.ned.dem.csiro.au/AGCRC/people/CoxSimon/