[Qgis-user] Guidance on matching property locations to WwTW catchments in QGIS

[Zouhair Ait Benali]

Morning everyone,

I just wanted to follow up on my query from yesterday and see if there are any updates. Please let me know when you get a chance.

Regards
 [cid:407fe35d-acda-40cf-b1fa-38451e2e8a3b]
Business Co-ordinator

zouhair.aitbenali at controlflow.co.uk

Office: 1c, Hylton Park, Sunderland, England, SR5 3HD

Visit our website - Controlflow<https://controlflow.co.uk/>

________________________________
From: Zouhair Ait Benali <zouhair.aitbenali at controlflow.co.uk>
Sent: 30 September 2026 10:07 AM
To: qgis-user at lists.osgeo.org <qgis-user at lists.osgeo.org>
Subject: Guidance on matching property locations to WwTW catchments in QGIS

Hello,
I am currently using QGIS 3.44 to map properties located within the Stodmarsh nutrient neutrality catchment and identify the wastewater treatment works (WwTW) catchment associated with each property.
The property locations have been imported using British National Grid eastings and northings, and the project is set to EPSG:27700. I have also imported WwTW catchment polygons, fixed their geometries and reprojected them to EPSG:27700.
I used “Join attributes by location” and “Extract by location” to match property points with WwTW catchment polygons. Most properties have been matched successfully; however, several properties near Charing WwTW fall outside the mapped Charing sewer catchment and therefore return no WwTW match. The affected properties include locations around the TN27 0DG , TN27 0DH / TN25 7AA ,TN25 7GR postcode areas.
Could you please advise:

  *
Whether “Join attributes by location” is the correct method for this assessment
  *
How I can check whether the unmatched properties are caused by coordinate accuracy, invalid geometry, gaps in the polygon data or incorrect CRS transformation
  *
Whether there is a recommended way to identify properties located just outside a WwTW catchment boundary
  *
Whether “Join attributes by nearest” should be used for initial screening while clearly recording that the connection remains unconfirmed
  *
Whether QGIS provides a method for identifying gaps or overlaps within the WwTW catchment layer

I understand that the final confirmation of the receiving treatment works would need to come from the relevant wastewater company. At this stage, I would like to ensure that the QGIS analysis and spatial matching have been completed correctly.
I can provide screenshots, sample coordinates and further information about the layers if required.
Kind regards,
Zouhair


 [cid:2047e347-c98e-440a-96a4-17efa40a6dde]
Business Co-ordinator

zouhair.aitbenali at controlflow.co.uk

Office: 1c, Hylton Park, Sunderland, England, SR5 3HD

Visit our website - Controlflow<https://controlflow.co.uk/>

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