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I followed the tutorial from http://schoolofdata.org/2013/04/27/creating-a-map-using-qgis The France map is from NaturalEarthData and tour de france data is from another source. They used different CRS (i.e., ED50 and WGS84 respectively).

I was wondering why the map and the data has different CRS? Is this usual in GIS?

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If you have on-the-fly-reprojection enabled, the layers don't need to have the same CRS. This is one of the benefits of good GIS software.

But beware, some operations like clipping need the involved layers to share the same CRS.

  • I was wondering why the map and the data has different CRS? Is this usual in GIS? – wannik Jan 1 '16 at 1:47
  • If you combine data from different sources, it is quite common. One party using degrees, others something in meters, old sources in feet etc... – AndreJ Jan 1 '16 at 6:43
  • Thank you for your explanation. One more question. How can on-the-fly projection knows which projection should be used? – wannik Jan 2 '16 at 4:40
  • Every GIS data comes with CRS information, or you are prompted for it. When activating OTF, you select a project CRS, to which every layer gets reprojected to. The project CRS can be set different from all layer CRS. – AndreJ Jan 2 '16 at 6:41
  • I thought that a vector layer contains lat, lng data. But if there is a CRS info in each layer, this mean that there are no lat & lng in a layer data, right? – wannik Jan 3 '16 at 4:12

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