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I've joined a csv file of values (0-100) (created in Excel), with local authority boundaries for the UK in ArcMap 10.1. I want to display the percentage of these areas not receiving 3G mobile coverage.

I've gone into properties and then selected quantities. I've selected the data I want to display and it displays huge values which are not in either the original data set or in the attributes table. Why is this? Here is a screen shot (note the range):

Screen grab 1

When I go into the attributes table for the selected variable ('t') and then sort descending, the largest value is 99. Why does it think there are values up to 1965621253?

Screen grab 2

I've not managed to find an answer online but so far I've:

  1. Checked that Excel isn't adding on extra values (I copied and pasted just the values numerous times)
  2. Generated a new csv file
  3. Tried to join the data numerous times to see if this made a difference.
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    Have you tried restarting Arcmap and do it all over again? Also, what if you look at the csv table from within Armap/catalog? It's not a decimal separator mixup?
    – Martin
    May 7, 2015 at 11:59
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    I have found that joined tables sometimes confuse ArcMap, as will null values. Workarounds include removing and redoing the join, doing the join in a new project and symbolizing it there before adding that to the original project, and exporting to a new feature class for symbolizing.
    – johns
    May 7, 2015 at 12:52
  • I would try adding a field and calculating it to equal "t". Then, remove the join and try to symbolize it off of the new field. Like @johns said, joined tables behave strangely sometimes.
    – GeoJohn
    May 7, 2015 at 13:53
  • I tried restarting Arcmap - same problem. I checked that there are no null values in the data set. I tried making a new project and repeating the join - same problem. I exported the shape files and did the join again - same problem. I finally tried to make a new field equal to the field I'm trying to symbolise. Still the same problem I'm afraid. Any other ideas?
    – Thirst for Knowledge
    May 7, 2015 at 17:00
  • What is the data type of the t field in ArcMap? Both as part of a Join and if you export the join result to a separate file? Is there any kind of numeric formatting on the field that might be disguising the true values? In attribute table right-click field heading and you can find the answer to both of these - it will tell you the type and you can click the ... numeric button to check that. Can you post files (or excerpts)/sources so we can try to duplicate?
    – Chris W
    May 7, 2015 at 22:54

1 Answer 1

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The classes seem to contain the values you want to display but have also ultra high ones. I have not a exact solution to your problem but some hints you could try.

  • Add the .csv file to ArcMap and export it as .dbf before joining. Add the .dbf to your workspace and try the join with this file
  • Alternatively open the .dbf files in excel and check if these high values occur in the table.
  • There could be a problem with the delimiter as well. As far as I know the standard delimiter of excel is different to the one of ArcMap. You could try to replace these delimiters with Notepad++ or similar before adding the .csv to ArcMap
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    Also try putting importing the CSV into a .gdb table. I find ArcMap works super well with these tables, so I use them a lot when I don't need to view or change them with other software. Also, it's improved, but Excel + ArcMap + joins is sometimes a little much to ask...
    – mr.adam
    May 7, 2015 at 18:53
  • Having opened the file in Notepad I found a null value that I hadn't seen in Excel. The join then worked fine and the problem was solved. Thanks for the help.
    – Thirst for Knowledge
    May 8, 2015 at 19:50

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