Python in ArcGIS Pro exercises

3.1   How to create add_field.py

Do you know how to export history to a Python script?

1. Using the same technique from this section, create a new folder called Field inside C:\PythonExercises.
2. Download Counties_Georgia.zip and extract the Counties_Georgia Shapefile into C:\PythonExercises\Field.
   • You should have C:\PythonExercises\Field\Counties_Georgia.shp and its auxiliary files in the same folder. I didn’t mean to extract all into C:\PythonExercises\Field\Counties_Georgia.
3. Add C:\PythonExercises\Field\Counties_Georgia.shp to the map.
4. Find the “Add Field” geoprocessing tool. Remember we’re not using the Field ⇒ Add icon in the attribute table.
   • Input Table: Counties_Georgia
   • Field Name: Test
   • Field Type: Double
5. Run.
6. Go to Analysis ⇒ History.
7. Right click on the “Add Field” history.
8. Save As Python Script to C:\PythonExercises\Field\add_field.py.
9. Open C:\PythonExercises\Field\field_stats.py in a text editor. Do you see this code?

   import arcpy
   arcpy.analysis.Statistics("Counties_Georgia", r"C:\Users\geni\AppData\Local\Temp\ArcGISProTemp30748\bfb83c98-7e80-4565-8e78-fc5db62d0f00\Default.gdb\Counties_Georgia_Statistics", "PopDens MEAN;PopDens STD", None)

   ))

   Edit
   Contents

   • 1   How to modify field_stats.py
   • 2   How to run field_stats.py
10. 1   Revisit Homework 1
    • 1.1   Calculate the areas of counties in $\text{km}^2$
    • 1.2   Calculate the population density in $\text{people}/\text{km}^2$
    • 1.3   Calculate the mean and standard deviation of the population density
    • 1.4   Calculate the population density category

1   How to modify field_stats.py

# we need the sys module to access arguments from the command line
import sys
# we need the arcpy module to run ArcGIS Pro tools
import arcpy

# overwrite existing files
arcpy.env.overwriteOutput = True

# path to a feature class as the first argument
fc_path = sys.argv[1]
# path to the output table as the second argument
table_path = sys.argv[2]
# field statistics to calculate as the third argument
field_stats = sys.argv[3]

arcpy.analysis.Statistics(fc_path, table_path, field_stats, None)

# NEW SYNTAX WARNING!!!
# open file for reading
f = open(table_path)
# print each line
for line in f:
    # each line from f already contains a new line, so don't print a new line
    # again (end='')
    print(line, end='')
# close file
f.close()

Edit

2   How to run field_stats.py

For output, you have to type .\ to create it in the current folder and use the .csv extension to be able to read it without using Excel.

python field_stats.py Counties_Georgia.shp .\totpop10_stats.csv "totpop10 MEAN; totpop10 STD"

Edit

1   Revisit Homework 1

Edit

1.1   Calculate the areas of counties in $\text{km}^2$

Use the same Counties_Georgia Shapefile from the above exercises, not the one you submitted for Homework 1 because the latter already has the SqKm field.

python add_field.py Counties_Georgia.shp SqKm Double
python calc_field.py Counties_Georgia.shp SqKm "2.58999 * !Sq_Miles!"

Did it work for you?

Edit

1.2   Calculate the population density in $\text{people}/\text{km}^2$

python add_field.py Counties_Georgia.shp PopDens Double
python calc_field.py Counties_Georgia.shp PopDens "!totpop10! / !SqKm!"

Did it (not?) work again?

Edit

1.3   Calculate the mean and standard deviation of the population density

python field_stats.py Counties_Georgia.shp .\PopDens_stats.csv "PopDens MEAN; PopDens STD"

Did you get this output?

FID,FREQUENCY,MEAN_PopDens,STD_PopDens
,159,72.526758495576033,143.460174992006614

FID is empty, FREQUENCY is 159, and the mean and standard deviation of the population density are $\SI{72.53}{\text{people}/\text{km}^2}$ and $\SI{143.46}{\text{people}/\text{km}^2}$, respectively.

Edit

1.4   Calculate the population density category

python add_field.py Counties_Georgia.shp PopDensCat Text
python calc_field.py Counties_Georgia.shp PopDensCat "'Low' if !PopDens! < 72.53 - 143.46 else 'Medium' if !PopDens! < 72.53 + 143.46 else 'High'"

Did it work?

NEW SYNTAX WARNING!!!

Nested ternary operators!

Here, we want to assign ‘Low’ if !PopDens! is less than $72.53 - 143.46$.

'Low' if !PopDens! < 72.53 - 143.46

Else we want to assign ‘Medium’ if !PopDens! is less than $72.53 + 143.46$.

else 'Medium' if !PopDens! < 72.53 + 143.46

Otherwise, we want to assign ‘High’.

else 'High'

Edit