Thiessen Polygon Total Area Calculations Model Builder/Python Code

Question

I am attempting to create a tool using Model Builder (and Python code) for calculating the average annual precipitation of a study area using the Thiessen Polygon Method. My model runs good other than finding the total area of the study area for further calculations in my model. Here is a sample of my code extracting the total area. I attempting to just use Summary Statistics to find the total area but I don't know how to access that table for input into further calculations.

def MySub (TotalArea1) :

 TotalArea = 0.0
 cursor = arcpy.SearchCursor(feat)
 for row in cursor:
    TotalArea += row.getValue("POLY_AREA")
 del row
 del cursor

 cursor = arcpy.UpdateCursor(feat)
 for row in cursor:
    row.setValue("TotArea", TotalArea)
    cursor.updateRow(row)
 del row
 del cursor

Answer 1

It seems your code sums the area covered by the polygons.

Instead of relying on a field that may or may not exist, and may or may not be correct you can get the area of the shapes at runtime:

Assuming that the feature class is in an appropriate spatial reference to sum the area:

def MySub(TotalArea1):
    TotalArea = 0.0
    with arcpy.da.SearchCursor(feat,"SHAPE@AREA") as sCur:
        for Row in sCur:
            TotalArea += Row[0]

    with arcpy.da.UpdateCursor(feat,"TotArea") as uCur:
        for Row in uCur:
            Row[0] = TotalArea

If not, say your data is in geographic coordinates and you want to sum in metres (or feet) simply project-on-the-fly:

def MySub(TotalArea1):
    TotalArea = 0.0
    toSR = arcpy.SpatialReference(28355) # MGA55, find a SRID that suits you
    with arcpy.da.SearchCursor(feat,"SHAPE@") as sCur:
        for Row in sCur:
            thisGeom = Row[0]
            projGeom = thisGeom.projectAs(toSR)
            TotalArea += projGeom.area
            TotalArea += Row[0]

    with arcpy.da.UpdateCursor(feat,"TotArea") as uCur:
        for Row in uCur:
            Row[0] = TotalArea

You will note the with statements.. these do not work for arcpy cursors, only arcpy.da cursors. When you declare a cursor in this way the disposal is automatic. You can of course use arcpy cursors with this method:

def MySub (TotalArea1) :
    desc = arcpy.Describe(feat)
    shapeFieldName = desc.ShapeFieldName
    TotalArea = 0.0
    cursor = arcpy.SearchCursor(feat)
    for row in cursor:
        thisShape = row.getValue(shapeFieldName)
        TotalArea += thisShape.area
    del row
    del cursor

    cursor = arcpy.UpdateCursor(feat)
    for row in cursor:
        row.setValue("TotArea", TotalArea)
        cursor.updateRow(row)
    del row
    del cursor

If you have a question about summary statistics please post that as a separate question.