Create sequential numbers in a field in ArcMap using Python in the Field Calculator based on longitude

[Sean_Wray]

I'd like to calculate an ID field (or some other numeric field) with consecutive numbers starting with 1. The order of this field will be based on the longitude field since I want to number my points from South to North.

I found this https://support.esri.com/en/technical-article/000011137 but it is based on the record number and not a field in the data. I have  put a portion of my table below.

Is this possible? This has stumped me for years!

[DavidHoy]

I dont have the code, but using python, you could create a list of all objectid,y values,

sort the list ascending (northern hemisphere) and then step through the list and update the corresponding feature's "ID" field

[AndyAnderson]

I assume you mean latitude rather than longitude if you want to order it from south to north?

If you don’t mind creating a new dataset, you can use the Sort tool:

https://pro.arcgis.com/en/pro-app/2.9/tool-reference/data-management/sort.htm

It will generate a new ObjectID in order of latitude (or any other existing field). Works both as a tool and in a script.

If you don’t want to generate a new dataset and your data is stored in a geodatabase, then you can create an UpdateCursor with an SQL ORDER BY … clause, and write an ordered index into a new field. This won’t work with a shapefile, though:

with arcpy.da.SearchCursor(data, "NewIndex", sql_clause=(None, "ORDER BY Latitude")) as cursor:

    index = 1    
    for row in cursor:
        row[0] = index
        cursor.updateRow(row)
        index += 1

https://pro.arcgis.com/en/pro-app/2.9/arcpy/data-access/updatecursor-class.htm

— Andy

[VinceE]

Just a note, you are using arcpy.da.SearchCursor in your code here, when I think you intended to use an UpdateCursor.