Can somebody please explain the difference of an ungeoreferenced scanned map and a georeferenced one in AutoCAD?


There are couple of differences that are coming to my mind. Shortest and simplest answer would be:

  1. Coordinates:

    • ungeoreferenced scanned map do not have coordinates in a coordinate reference system that the software can understand. They will be pixel values relative to a local 0,0. That means the program cannot locate the map in real world. You can think about it like a photo you have on the wall. It looks familiar but you have no idea where it was taken.
    • georeferenced scanned map has coordinates relative to a known coordinate reference system. When you load the map, the program can identify where it is in the real world.
  2. Scaling:

    • ungeoreferenced scanned map is not using meters or a other unit of measure (besides pixel size), which means you cannot measure anything on it and your map is misshapen. Without correct scale and coordinates, measuring distance or area is not possible.
    • georeferenced scanned map has coordinates assigned including a unit of measure. When you load the map, the program can measure things like distance, area, etc. What is more, objects on the map are located where they are in the real world.

So in general you cannot do GIS analysis on ungeoreferenced map as digitization, distance measurements or spatial functions will not work on them.

Probably there are more differences but these are the most obvious ones.

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