I received a set of drawings that were drawn in millimetres but in the correct coordinate system; I use GDA94 with my coordinates in metres, so this should theoretically be a simple fix using my usual process:

  1. UNITS > change 'millimetres' to 'metres'.
  2. Select all > SCALE > base point 0,0 > .001 scale factor

Once this is done, checking the coordinates on the status bar on AutoCAD indicates that my data is in the correct scale and coordinate system, but once I bring it into ArcGIS, it projects nowhere near where it's meant to go and with coordinates that probably aren't even in the same coordinate system.

What is happening? I've used this method before and it usually works, I'm not sure what's happening in this case.

EDIT: the coordinate system I am using is a variation of GDA94 (Perth Coastal Grid 1994). A centre point in the CAD drawing shows a coordinate of 59501 E, 273281 N, which is correct for my purposes. However, zooming to the same layer overlayed in ArcGIS produce a central coordinate of approximately -845 E, -3346 N -- the data doesn't even display, but it could be due to CAD hatching not importing.

  • Please Edit the question to provide more complete spatial reference information on the declared .prj/EPSG that was provided to ArcGIS.
    – Vince
    Apr 15, 2019 at 11:43

1 Answer 1


If arcmap is giving you unkown projection, then you need to apply define projection tool.

  • No, I have the projection in ArcMap. The projection is defined as GDA 1994 - Perth Coastal Grid 94. My native GIS data projects fine, CAD data I have produced in ArcMap and opened in AutoCAD projects fine and overlays over the CAD file I'm trying to bring in. However, the CAD file I'm trying to bring in does not overlay properly in ArcMap.
    – tathlum
    Apr 16, 2019 at 5:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.