I am trying to spatially join point layers of some 12,000 women interviewed in Egypt to Egypt's polygon layers (administrative districts boundaries) using QGIS 2.2 and need some advice. I am a QGIS self-learner.

I have read many QGIS manuals, but I cannot complete the spatial join successfully. I have added the vector layers of both Egypt's women's GPS points and Egypt's polygons (district boundaries). I used the UTF-8 encoding. Whenever I attempt to join attributes by location, the following message appears "Input layers have non-matching CRS". However, when I check the CRS of both layers, I found it the same (EPSG:4326 - WGS 84).

  • How have you checked the CRSs? Are you able to view both layers properly overlayed? – MickyInTheSky May 29 '14 at 7:56
  • I have checked the CRSs by right clicking each layer, choosing the Properties tab, then choosing the General tab. I cannot view both layers properly overlayed. However, I can see each layer properly when I separately open it. – Amira El-Shal May 29 '14 at 8:07
  • Tho QGIS is trying to use EPSG:4326 in both layers, they are actually not the same. You should check with your data origin what is the real CRS of the files. For Spatial join work properly both layers must overlap. – Alexandre Neto May 29 '14 at 8:41
  • which Spatial Join tool are you using in QGIS? – HDunn May 29 '14 at 8:44
  • I click the Vector tab, then click the Data Management Tools tab, then select "Join attributes by location". – Amira El-Shal May 29 '14 at 8:59

After being reasonably certain of the correctness of the CRSs (check also the on-fly projection option) you could use the spatial query plugin

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  • I know the CRS of one shapefile but the coordinate system of the second layer is unknown, and there is no *.prj file. How I can identify its CRS? – Amira El-Shal May 29 '14 at 10:53
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    You can define it with the following Qgis command: Vector--> Data Management Tools--> Define Current projection – MickyInTheSky May 29 '14 at 10:57
  • I could not save the women's locations to a new layer, using the CRS of the administrative districts boundaries, because I do not know the CRS of the boundaries. No *.prj file is there and I do not have access to the supplier in the meantime. I just know the CRS of the women's locations. Therefore, I tried to save the boundaries to the CRS of the interview locations then do the spatial join, but it did not work either. What is your advice? – Amira El-Shal May 29 '14 at 11:42
  • it's very hard to do a spatial join with a layer with unknown CRS. I would recommend you open a new post – MickyInTheSky May 29 '14 at 12:00

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