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I am trying to identify multipart features using QGIS version is 1.8.0.

I've tried:

  1. look at the attributes table
  2. select a random feature and check in the canvas if there are multiple geometries selected
  3. repeat until found one or all features have been examined

What I would like to check is something like a Boolean value in the Layer properties!

  • Which Version and what have you tried to find multi-part features? – Mapperz Oct 24 '14 at 17:02
  • The version is 1.8.0 and what I tried is : 1) look at the attributes table, 2) select a random feature and check in the canvas if there are multiple geometries selected, 3) repeat until found one or all features have been examined. – user2302585 Oct 24 '14 at 17:07
  • please put this info in your question to be re-opened. – Mapperz Oct 24 '14 at 17:10
  • Ok, done.. sorry! – user2302585 Oct 24 '14 at 17:52
  • If I recall this can be done with a simple field calculation in ArcGIS, but I don't know about QGIS. If you only want to identify them, you could make use of the Topology Checker plugin and use the 'must not have multi-part geometries' rule but I believe that will require a newer version of QGIS. If you're ok with breaking them up rather than just identifying, there's the multi-part to single-part tool, though again that may require a newer version. – Chris W Oct 24 '14 at 21:02
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I'm on QGIS 2.4; not sure if this will work in 1.8!

Start an edit session on the layer and add a new field called multi - an integer, single-digit.

For the expression, enter:

CASE WHEN  geomToWKT( $geometry ) LIKE '%MULTI%' THEN 1 ELSE 0 END

This will give you a 1 for each row when it's a multi-part line or polygon.

  • It seems that geomToWKT( $geometry ) gives NULL, I was looking up for a sort of reference to discover when this happens but I found nothing. can you please explain me this ? – user2302585 Oct 26 '14 at 10:41
  • I suspect that's happening because of the older version (1.8). Why not upgrade to 2.4? Basic functionality the same but far, far more features and much better performance. – Simbamangu Oct 26 '14 at 11:24
  • This is pretty much what I was thinking of for ArcGIS, except the expression uses !shape.isMultipart! - I didn't know how to do that in QGIS, and it appears the version might play a role as well. – Chris W Oct 26 '14 at 20:07
  • I was trying avoid the version switching to keep the one which my Professor used during the lectures, but I ended up doing it anyway. Thank you very much. – user2302585 Oct 27 '14 at 16:38
  • It's a pretty significant upgrade in terms of capability and performance - and I doubt that much will be different to the one used in your lectures. Thanks! – Simbamangu Oct 27 '14 at 17:19

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