1

enter image description here

enter image description here

enter image description here Trying to use the v.buffer function to create a 500-foot buffer (map units are in metres, which is why I put 152.4 meters as the buffer distance) around the boundary of a property parcel (not the centroid). I'm unsure what to populate the "'Category values' and 'WHERE conditions of SQL statement without 'where' keyboard'. All I want to do is create a 500-foot buffer around the parcel boundary, so I am finding a lot of these fields don't apply to me. When I try to run what I have entered, I get the error that there are not enough arguments.

1

Yes, the WHERE conditions should not apply to your case, but unfortunately we cannot escape from this keyword - it is mandatory as far as I know.

I usually set a dummy (meaningless) condition, such as "ID" > 0 or "ELEVATION" < 1000000 so that the conditions always return TRUE.

[Example] - Natural Earth dataset

Ir has a "scalerank" field which is always 1, so I can set "scalerank" > 0 into the where condition.

enter image description here

Then v.buffer runs smoothly and returns output like below:

enter image description here

Many GRASS vector commands demand this WHERE clause - but I honestly do not know why.

  • Thank you! This is very helpful. So what do you enter for the category values then? – sophiasmarand Jun 7 at 21:47
  • @sophiasmarand I leave the category values blank. – Kazuhito Jun 7 at 22:25
  • It might be worth noting that the where= parameter is not mandatory when running this module in GRASS itself. – Micha Jun 9 at 12:34
  • Absolutely, thanks @Micha - Hope this can be fixed in QGIS interface soon. – Kazuhito Jun 10 at 17:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.