[GIS] Symbolizing layer with graduated colors by date/time field

arcgis-9.3arcgis-desktoparcmapsymbology

I've got a layer of polygons where each has a date associated with it. I want to color the polygons with graduated colors, but I want the colors to start with the newest polygons and fade to the oldest polygons. So far I haven't been able to find a way to do this in ArcMap (<= 9.3.1) other than to create a new field and calculate some integer or float value based on the date. Is it possible to use a date or time field directly?

The data is natively a date-time value
There are far too many records to use any unique-value renderer
Converting the date to a numerical field is an answer for a different question.

Best Answer

If you are looking for Quantities -> Graduated Colors/Symbols, they won't directly work with Date fields. You could however convert the date fields to numbers and use that instead. I'd convert each date to an Epoch timestamp (number of seconds since a particular date, 01/01/1970 being used most frequently), then use the Epoch timestamp to symbolize your features.

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I don't think you can use SimpleRendererClass because it is designed to use the same symbol for all features. You might want to take a look at ClassBreaksRendererClass.

SDK page for ClassBreaksRenderer

It also has "see also" links to other types of renderers that may be appropriate.

ArcGIS Date Field Conversion – How to Transform ArcGIS Date Field to Integer

I suggest that you use strftime('%Y%m%d') in the field claculator.

Just for the sake of completeness, your method is not very "pythonic" but it seems correct. However,the wrapping of your python code block as shown on your post looks incorrect. Unlike with VB, you need to define a fucntion in the code block, and call it in the field calculator.

code_block_function(!ACQ_DATE!)

in the code block, use:

def code_block_function(a):
    date=str(a)
    year= date.split("-")[2]
    month= date.split("-")[1]
    day= date.split("-")[0]
    dateInt= int(year) * 10000 + int(month) * 100 + int(day)
    return dateInt

Best Answer

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