Expression to define symbology

GIS_Ecologist — Thu, 06 Jul 2023 13:12:02 GMT

Hello all,

I am working on a habitat mapping feature layer and need to write an expression to exclude null fields.

I have the layer setup with 5 fields utilising contingency selects (which is also not currently working on ArcGIS online but is on fieldmaps and pro). I need the symbology to select the field with a non empty cell to generate the appropriate symbology for that field.

I have build it as below with 5 levels of habitat characterisation of which I need it to be weighted to level 5, by which I need it to select the furthest right value which isn't null.

Any help on this would be much appreciated. I am fairly new to writing expressions and don't really know where to start.

Thanks and look forward to seeing your replies

Re: Expression to define symbology

MicZatorsky_AEC — Thu, 13 Jul 2023 02:44:29 GMT

Add a field to store the value you want to use with Unique Values symbology e.g. "symbol_class"

Then populate that field - if there is a Level5 value, use it, else look at the previous levels until you either have a class or there is none. Since you may have nulls or spaces, or empty strings, handle those too.

The code for determining the class to use for symbology would be:

def getSymbolClass (Level1,Level2,Level3,Level4,Level5 ):
    if Level5 is not None and str(Level5).strip() != "":
        return Level5
    if Level4 is not None and str(Level4).strip() != "":
        return Level4
    if Level3 is not None and str(Level3).strip() != "":
       return Level3
    if Level2 is not None and str(Level2).strip() != "":
        return Level2
    if Level1 is not None and str(Level1).strip() != "":
        return Level1
    else:
        return "no class"

Used in the context of CalculateField:

arcpy.management.CalculateField("test", "symbol_class", "getSymbolClass(!Level1!,!Level2!,!Level3!,!Level4!,!Level5!)", "PYTHON3", """def getSymbolClass (Level1,Level2,Level3,Level4,Level5 ):
if Level5 is not None and str(Level5).strip() != "":
return Level5
if Level4 is not None and str(Level4).strip() != "":
return Level4
if Level3 is not None and str(Level3).strip() != "":
return Level3
if Level2 is not None and str(Level2).strip() != "":
return Level2
if Level1 is not None and str(Level1).strip() != "":
return Level1
else:
return "no class" """, "TEXT", "NO_ENFORCE_DOMAINS")

Repace "Test" with the name of your layer.

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Expression to define symbology

Re: Expression to define symbology