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I need to create a thematic map for time intervals (ex. 1/1/1920-31/12/1929). To every polygon corresponds a date (from a date field) and I need them to be coloured depending in which interval they are situated. I can't find anywhere in the symbology tab a place to type the time ranges. In the quantities section I can't even select any field.
I would like to use Field calculator to convert my date into a number, which would represent the first year of a decade. For example 20/9/1954 ->> 1950. I think that would help me a lot. But I don't know how to do it in python or VB.
I have access to the Excel table that has been attached to the shapefile and I could easily do this transformation in Excel. And then add the data again to ArcMap. But I prefer doing it all this in ArcMap.
Another problem is that I have dates prior 1900, and if I sort them ascending, the ones before 1900 would appear even before the null values. So I guess ArcMap doesn't recognize them because of Excel. I've already read another topics about this problem, but I still couldn't find a solution.
I also read this answer to a similar question:
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.
That would be very helpful too, but again, my lack of programming skills blocks me.
I solved this by extracting the year from the date field into a new field (integer) using field calculator and the formula: DatePart ("yyyy", [field.name] ). And then I created the map by quantities and used the intervals I wanted.