I'm just starting using QGIS. I have run a couple of geoprocessing tasks and the results look good but I'm trying Union and am not having much success.

The main one I'm trying to do is, I have a city corporate boundary and two types of road data - road centerlines and ROW boundaries. I am trying to union the corporate boundary with each one separately, and in both cases, when I run it the resulting shapefile seems to be empty.

The original vector files (roads and corporate boundaries) are all from geodatabases and the output is shapefile.

Any assistance would be help, maybe it's already been covered elsewhere here and I just didn't see it.

enter image description here

enter image description here

Ok, that seemed to work. See below.

enter image description here

Now, my next step is I'm trying to polygonize. But I'm getting an error message. Basically what I'm trying to do is divide the city into blocks so I can assign a value to each block. Maybe I should post this as a separate topic but I'll try here. I'm not sure if I'm getting the error because of something about the lines or someting in the attribute table... Or something else. Here's a closeup of what the street centerlines look like.

enter image description here

Maybe I need to clean up the lines or something, not sure. But anyway here's the error message I get when I run it.

enter image description here

  • 1
    What do you mean by "ROW boundaries"?
    – Pura Vida
    Apr 24, 2017 at 2:49
  • 1
    Welcome to GIS SE! As a new user please take the tour to learn about our focused Q&A format. Can you please edit your question to include a screenshot of sample area showing your centerlines and ROW boundaries? What are "ROW boundaries" - does ROW stand for Right of Way?
    – Midavalo
    Apr 24, 2017 at 3:17
  • I'll try to get some screenshots here soon. Yes, right of way boundaries.
    – GDog
    Apr 26, 2017 at 1:32
  • For those asking, ROW means Right of Way, the entire area of the road lanes, shoulder, sidewalks and ditch.
    – HDunn
    Apr 26, 2017 at 5:14
  • "Maybe I should post this as a separate topic but I'll try here." You should only post this as a new question because this is a focused Q&A site. Please cut/paste the new question into a new question.
    – PolyGeo
    Apr 28, 2017 at 20:14

1 Answer 1


Your roads and corporate boundaries are polylines. As such, a union would only work for line segments which are identical. enter image description here

You need to convert your boundary data to polygons, using the Lines to Polygons tool (or similar), and then perform the union with the resulting corporate boundary polygon.

enter image description here

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.