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I am trying to georeference raster sketch maps that have polygons drawn on them to line up with vector polygons. Its relatively easy to do this using the georeferncing toolbar in arcmap for 1 polygon, however once there are 2 polygons it becomes much more difficult to get it accurate. Does anyone have any experience with this? See image attached.

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  • It may be impossible to get the two to line up. A sketch implies rough or not to scale. It will definitely be Cartesian/planar. You don't give any info on your polygons - were they created by inputting dimensions from the sketch? What coordinate system are you working in, either to do the georeferencing or that the polygons were created in? At best you may be able to increase the number of control points and complexity of the transformation. See resources.arcgis.com/en/help/main/10.1/index.html#/…
    – Chris W
    Commented Jun 4, 2015 at 20:42
  • Coordinates were obtained in field using gps and wgs84 and supposed to be drawn roughly to scale. Georeferencing done in wgs84.
    – JHam
    Commented Jun 5, 2015 at 7:34
  • GCS WGS84 is an ellipsoidal coordinate system, whereas your paper is flat. While you would want to enter your GPS coordinates in that CRS to create the shapes, unless you then project that to a projected coordinate system (like UTM), you're going to have distortions between the two. If you want to stay in WGS84, you'll need to use a more complex transformation - second/third order polynomial, or spline. This is because you actually need to warp things from flat to curved (unproject), not just shift/scale/rotate them. Again, the help linked in my first comment would be a good read.
    – Chris W
    Commented Jun 5, 2015 at 19:47

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Since there are two polygons it will be hard to obtain an accuracy that puts the two polygons at their exact locations, I suggest you use 2 points from the each polygon, so that you obtain an average like score of the two.

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