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I have three shapefiles and two buffers made from two separate shapefiles. I was trying to do a spatial join and it kept coming up with an empty file even though there was clearly overlap. I realized that some of the shapefiles had different projections. I changed them all to NAD 1984 for zone 18 and I also tried WGS, and then GCS WGS, but two of the shapefiles and a buffer file are now unaligned with a shapefile and its buffer. They are all the same coordinate system and they aren't aligning when they were before I changed the coordinate system. Is there a way to change them back? The undo button just says "remove layer." Or suggestions to fix this? I don't want to start from scratch with the original data.

PolyGeo
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Sams
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1 Answers1

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If you are defining the projections with define projection or editing their properties then you will encounter this problem. What you want to do is Project to the coordinate system. This will modify the features to be in the new coordinate system and not just redefined and in the same place.

To define them back again just do what you did before in reverse.

Michael Stimson
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  • I was using define projection. I'll try your suggestions now. There was two or three projections and I can't remember which ones they were originally and it wasn't in the metadata. I think one of them was unknown. – Sams May 18 '14 at 22:17
  • Unknown is bad. There are assumed coordinate systems that ArcGis uses if it's unknown, but you can't really project from that. It has to be something to project from. Did you perchance keep a backup? – Michael Stimson May 18 '14 at 22:19
  • @Sams If you have no backup then there are some suggestions for dealing with unknown/uncertain coordinate systems at http://gis.stackexchange.com/questions/7839/best-practices-for-identifying-the-unknown-coordinate-system-of-a-shapefile – PolyGeo May 18 '14 at 22:21
  • No, I didn't think to make a backup. – Sams May 18 '14 at 22:22
  • @MichaelMiles-Stimson I tried your original suggestion and it doesn't seem to have made a difference. – Sams May 18 '14 at 22:24
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    Try closing ArcMap and start again with a fresh ArcMap session. – Michael Stimson May 18 '14 at 22:44
  • I got the same data from a different source and now the project suggestion from earlier and it seems to be working. Thanks for the help! – Sams May 18 '14 at 23:11
  • As often as this comes up, I think ESRI should add a warning dialog to that tool - "Are you sure you want to DEFINE the projection? This tool does not REPROJECT. It is intended for assigning a projection to data that is undefined or incorrectly defined." Or maybe they should just change the word Define to Assign in the tool name. – Chris W May 18 '14 at 23:51
  • Agreed, it's one of the more common problems I encounter. That and NOT assigning the correct projection. I had a whole project captured as GDA94 but the data was really in AGD66... (207m NNE different) fortunately a define & project saved the day! – Michael Stimson May 18 '14 at 23:57