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I'm having trouble with the projection of one of my shapefiles (it's the roads network of the region I'm working on). I have a shapefile without any spatial reference information. When I use the define projection tool to assign it the same coordinate system as my other shapefiles it doesn't line up as it should.

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    If they don't align, it's a mistake to define the unknown layer in that coordinate system. – Vince Sep 27 '18 at 20:40
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That means it's not in the same coordinate system as your other shapefiles. You have a few options:

  1. Go back to the website or person where you got the shapefile from and ask/search for metadata.
  2. Trial and error: start assigning different coordinate systems until you find one that works. Since it's a road network, compare it to a basemap to figure out when the roads are in the right place.
  3. If all you need is a basic road network, you can probably download one with a properly defined coordinate system from open street maps or the regional government (in the US, try the state department of transportation).
  • as @csk said, the best approach is to assigned different projections to it until it lines up with a layer which you know is good. There are some more specific details about the approach at this link, as well as some tips to speed up the trial / error. desktop.arcgis.com/en/arcmap/10.3/guide-books/map-projections/… – Marshall Sep 27 '18 at 21:16
  • The best approach is to find out what projection it's supposed to be in. Trial and error is a last resort if the data provider failed to provide metadata in any form. – csk Sep 28 '18 at 14:04

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