I have a tank age data set which I would like to present on ArcGIS.

I would like to represent the different tanks using their tank age. I would like the symbol colour to be dependent on the tank age (think red, green, yellow).

The problem is, there are some tanks which I don't have the tank age for.

How can I represent the tanks that don't have tank age?

Should I:

  • Put in the tank age as 'N' to give it a character input
  • I can't put a dummy number such as -9999 since I have other graphical representations that rely on that age field and -9999 would skew the charts.

Edit: - I could create a different column for Null_values and ask the symbology to draw off that. I'm unsure if we can represent one symbology from different fields. - Grey of blank would be a great visual but I'm not sure how to map off the NULL data.


Raw Data

Symbol definition

  • Is your question about how to symbolise it, or how to record it in your data? – Midavalo Nov 13 '17 at 22:28
  • How are you trying to symbolize them? Is tank age a numeric, date or character field? Perhaps you can split the layer into two layers by definition query (tank_age is not NULL and tank_age is NULL) give one an age symbology and the other a single symbol. – Michael Stimson Nov 13 '17 at 22:28
  • Hi Michael, thanks for your reply. Always good to get your input. I guess that is one way to do it, although not as efficient, since I will need an extra field, and any reports I do afterwards might have that 'gap'. The link below sums up what I'd like to do. gis.stackexchange.com/questions/241284/… – ShekieD Nov 13 '17 at 22:29
  • I like the absence of color to represent the absence of data: white, black, or a gray color. – Dan C Nov 13 '17 at 22:30
  • 1
    @DanShek Can you also show how you've defined your symbology? Why can't you use NULL as another symbol option? – Midavalo Nov 13 '17 at 22:56

Create an exclusion in your symbol classification. In your Layer Properties > Symbology tab, click Classify. In the Classification dialog click Exclusion:

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On the Query tab, add an exclusion for your NULL values:

Tank_Age IS NULL

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Change to the Legend tab and check Show symbol for excluded data

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Now your NULL values will show as symbolised. You can symbolise them however you want here.

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