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Has anyone had the problem that the scale of the shp layer converted originally from a .dxf file turns out to be wrong?

For example, I draw a line of 10 meters long in AutoCAD and imported it in QGIS, however the length of this line turns out to be several thousand kilometres.

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    You must import the data into some metric projection, for example UTM. I am pretty sure that you have converted your meters into degrees latitude/longitude (and QGIS has projected that in-a-fly into the projection of your QGIS project).
    – user30184
    Jul 27, 2014 at 18:02
  • Hi 30184, thank you very very much! According to you suggestion I have tried to set in QGIS the CRS to some "Projected Coordinate Systems". As I have a google satellite
    – yang
    Jul 28, 2014 at 8:57
  • However, the area of the maps that I am working on is Beijing, China, and when imported, the vector geometry appears at somewhere in Africa. When I tried to move the geometry to Beijing(I saved the layer as .shp and used the "move features" function), the scale changed. For instance, the original 100m line in Africa is only 76m when moved to Beijing. I tried to set other CRS, but still cannot manage it. I'll keep on trying though.
    – yang
    Jul 28, 2014 at 9:49

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Google satellite (EPSG:3857) is not a good idea. The units are metres, but only at the equator. The more to the North you go, the greater the difference gets.

Alternatively, you can use a custom CRS in transverse mercator projection, with latitude and longitude of origin (in degrees) at the point where your dxf file has its origin:

+proj=tmerc +lat_0=... +lon_0=... +x_0=0 +y_0=0 +k=1 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs
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