I am merging two layers, a data file and shapefile based on spatial location.

I am doing a many to one type join and I want my attribute to take a summary of the intersecting features, using mean data.

When the join takes the mean of attributes I want an answer with decimal points. It should be a messy number like 3.8739 but instead it rounds up or down so I get 3 or 4. I suspect this has something to do with the 'Precision' feature but I don't know how to use it!

For 3 decimal points do I want a precision of 3.00000?

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2 Answers 2


Your guess about the Precision ist correct! A Precision of 3 will result in a number with three decimal digits, e.g. "n.nnn". Some more examples on "precision" and "width" (the latter is not available/necessary in your context): Manually Adding a Decimal Field to the Attributes Table

  • Thanks @Flo F. So to be a little dense, what would be the difference between putting 3.000 and 3.333?
    – Henry Cann
    Commented Feb 3, 2017 at 10:54

In addition to the @Flo F.'s answer, it turned out it was also necessary to change the source format, strangely.

For example formerly all my values were single integers without decimals. I went and changed the original CSV source so that even though they were still all whole numbers, they appeared in the format 4.0000 rather than just 4.

Only once I did this did it give me correct decimals in my join output.

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