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Why do I can't do union or do another geoprocessing two shapefiles with different CRS in QGIS? For example, I want to do union two shapefiles, one shp with CRS WGS84 and another shp with CRS WGS84/UTM 47N. It can't be happened and a message box will appears. Even though this process can be done in ArcGIS. I'm using QGIS 2.14 Essen. Any suggest?

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    ArcGis reprojects the files before the processing takes places as well, but temporary. Thats kind of a inbuilt convenience option to the user that does not need to take care and only gets the output. Qgis did not implement this extra step in the tools. Maybe it will be at some point. – Matte Jun 17 '16 at 9:24
  • Ah...I see. But, when I reprojects the layer first in QGIS, then the layer be located to different location that far away from the first one. – Dias Jun 17 '16 at 9:40
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QGIS works for defined projection in each layer and does not work with layers with different projections. Even if you see the two layer overlay each other due to the on fly projection is enabled, the on fly projection in QGIS does not disable the original projection defined in the layer. Therefore, if you want to do any geoprocessing task, the two layers should have the same projection in order to get a successful result.

You can simply right click one of the two layers and go to save as, and in the 'save as' dialog box choose the target projection which should be similar to the second layer. Then do the geoprocessing task that you want.

  • If I save the layer 1 to the same CRS with layer 2 then the layer 1 will appear on different location with layer 2. I have no idea why it happen. – Dias Jun 17 '16 at 9:28
  • Create a new QGIS project file and load your data (both layers) in the new project file. – ahmadhanb Jun 17 '16 at 9:40

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