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I have just converted some British National Grid coordinates to degrees decimal, WGS 1984. I now want to do the same with a UK local authority shapefile which I have read into a couple of different programs and which doesn't make any sense to me. The only info in the shapefile is 'Geo_code'. I presume I need to convert the shapefile to the same notation system but I don't understand the format it is currently in. Unfortunately trying to convert the shapefile in ARC Tools gives an erro.

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You don't need to have coordinates in the attribute table for the shapefile to be usable. In fact, sometimes you don't want coordinates as attributes because you would need to continually recalculate them if you're doing a any geometric editing of the shapefile.

Does the shapefile have a defined coordinate system? Check its property page. If it doesn't, try adding it to ArcMap with some other BNG data, or even with the WGS84 data. Set the data frame to BNG. Does the local authority data line up? If it does, define its coordinate system as British National Grid. Then use the Project Tool to convert it to WGS84.

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  • Thank you both. I followed the instructions to convert the shapefile to WGS84. Seems good, However what's strange is my excel imported data doesn't plot onto the map at all. I can't get it to show any representation overlayed on the map whatsoever since I made this change to the shapefile. What might have happened? Thanks – Henry Dark Aug 9 '16 at 22:20
  • Add the original into a new arcmap and check its extent via mouse or status bar. Please edit the question with the values. – mkennedy Aug 9 '16 at 22:23
  • Done - I hope that's what you meant. (went back to the original shapefile and checked extent. The original of course is listed as BNG – Henry Dark Aug 9 '16 at 22:50
  • When you added the XY data into ArcMap, if ArcMap's data frame's coordinate system was WGS 1984, that would have been assigned by default to the XY data. Try adding it again, but change the coordinate system in the Add XY tool to British National Grid. – mkennedy Aug 10 '16 at 0:22
  • At that point, if there's a transformation set to convert from BNG to WGS 1984, right-click the layer and select data, export data. Set it to use the data frame's coordinate system (WGS 1984) and export the data to shapefile or feature class. – mkennedy Aug 10 '16 at 0:23
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Assuming these are point locations:

Create two new fields called x and y, or something of the like. Then, right click in those fields in the attribute table, choose Calculate Geometry, and then the appropriate coordinate type (x or y) for each field. That will explicitly record into the attribute table the coordinates for each point in whatever spatial reference system the data is in.

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