Research Question

Did Tsetse flies cause Africa's poverty?

Important?

• Tsetse flies, found only in Africa, kill livestock
• Believed to be a historical cause of Africa's low agricultural productivity & high transportation cost
• Path dependence may explain Africa's poverty today

Original?

• No systematic evidence on the impact of Tsetse flies
• Find Tsetse flies prevented political centralization

Feasible?

Data Sources

Ethnographic Atlas + Murdock (1959)'s map

• Pre-colonial data on use of domesticated animals, presence of intensive agriculture, political centralization

Weather at 2°x2° grid cells in 1871 from 20th Century Reanalysis Project

• Mean temperature
• Mean humidity

Climate factors of Tsetse Survival

(Figure 2 of Alsan 2015)

Feed temperature and humidity into the these curves

$\Rightarrow$ Tsetse Suitability Index (steady-state population)

Tsetse Suitability

+

Ethnic homelands

We will learn how to match these two data

Empirical specification

$$\begin{align*} Y_j = \alpha + \delta TSI_j + \boldsymbol{X}'_{j}\boldsymbol{\omega} + \varepsilon_{j} \end{align*}$$

Main Results

(Table 1 of Alsan 2015)

we will learn how to:

1. Use the Spatial Join tool (Exercise 2)

2. Export attribute tables to Stata (Exercise 3)

3. Create grid cell polygons (Exercise 1)

Why grid cell polygons?

In natural science data (e.g. weather data),
the unit of observations is often a grid cell.

• Partly because they derive data from satellite images

Examples:

• GCPC: time-series of precipitation (2.5-deg)
  • used by Miguel et al. (2004)
• WorldClim: cross-section of monthly weather (30-sec)
  • used by Dell, Jones, & Olken (2009)
• CERSAT: wind speed and direction in oceans (1-deg)
  • used by Pascali (2017)

Grid cell polygons help merge these data with other data

Exercise #1: Overview

Create 20th-century Reanalysis data grid cell polygons

We will use 3 geo-processing tools for this exercise:

1. Create Fishnet
2. Define Projection (Data Management)
3. Add Geometry Attributes

As in Lecture 1, we use these tools in Model Builder.

1. Create a Model
2. Save it as code/lecture2.tbx/exercises1-3

Exercise #1: Overview (cont.)

20th-century Reanalysis data

Spatial resolution: 2° x 2°

Africa: roughly spans within

• 40° S to 40° N
• 20° W to 60° E

$\Rightarrow$ Create square polygons whose centroid is from (-20°, -40°) to (60°, 40°) at the interval of 2°

Exercise #1: Step 1

Create Fishnet

Output Feature Class: ...\Lecture2\temporary\fishnet.shp

• Save all intermediate outputs in the temporary/ folder

Fishnet Origin Coordinate

X Coordinate: -21

Y Coordinate: -41

$\Rightarrow$ Bottom-left polygon's centroid will be (-20°, -40°)

Create Fishnet (cont.)

Y-Axis Coordinate

X Coordinate: -21

Y Coordinate: -10 (or any value other than -41)

$\Rightarrow$ Y-Axis will be perpendicular to the horizontal X-Axis

Number of Rows: 41

• (40-(-40))/2 + 1 = 41

Number of Columns: 41

• (60-(-20))/2 + 1 = 41

Create Fishnet (cont.)

Uncheck "Create Label Points"

• Label points: unnecessary for our purpose
• Model Builder will still show label points as an output from Create Fishnet. This is a bug.

Geometry Type: POLYGON

• By default, this option is set as POLYLINE. Make sure to change it.

Exercise #1: Step 2

The Create Fishnet tool doesn't assign any coordination system to the output file

Ethnographic Atlas data uses geographic coordinate system

$\Rightarrow$ Assign WGS 1984

How? We already learned this in Lecture 1 Exercise 6.

Exercise #1: Step 2 (cont.)

Define Projection (Data Management)

Input Dataset or Feature Class: fishnet.shp

• Use the drop down menu to choose the output from Create Fishnet

Coordinate System: GCS_WGS_1984

• Click
• Navigate to Geographic Coordinate Systems > World > WGS 1984

Exercise #1 (cont.)

Now save and run the Model.

Browse the output.

Overlay the Ethnographic Atlas data

• .../Lecture2/input/tribemap.shp

20th Century Reanalysis data cell polygons should cover the whole mainland Africa.

Exercise #1: Step 3

Browse the attribute table of the output (cf. Lecture 1)

We don't see centroid coordinates to match with weather data...

$\Rightarrow$ Use the Add Geometry Attributes tool

Exercise #1: Step 3 (cont.)

Add Geometry Attributes

To add the centroid coordinate values in attribute table

Input Features: fishnet.shp (2)

• This is the output from Define Projection
• Don't choose fishnet.shp (which is the output from Create Fishnet)

Geometry Properties: check CENTROID

• The CENTROID_INSIDE is for hollow polygons

Note: this tool overwrites the input file

Exercise #1 (cont.)

Now save and run the Model.

Browse the output and its attribute table.

Is everything as expected?

Exercise #2: Overview

Merge ethnic homelands
with 20th Century Reanalysis cells

Ethnic homelands: polygons

How to match polygons with polygons?

• One polygon can overlap with several polygons
• Which one to pick? How to aggregate them?

One way to go: match polygon centroids with polygons

Exercise #2: Overview (cont.)

Polygon centroid

Mean position of all points on the polygon boundary

(Image source)

$\Rightarrow$ Can be matched with a single weather data grid cell

Exercise #2: Overview (cont.)

1. Create ethnic homeland centroid point features

• We have XY data in the attribute table of the ethnic homeland polygon (.../input/tribalmap.shp)
• Which geo-processing tools should we use?
• hint: Lecture 1 Exercise 3

2. Use Spatial Join to match ethnic homeland centroids with 20th Century Reanalysis grid cells

We now add these processes to the Model for Excercise 1

Exercise #2: Step 1

Make XY Event Layer

XY Table: ...\input\tribalmap.shp

• Note this tool can be used for shapefiles

X Field: tribelon

Y Field: tribelat

• These two variables were most likely to be created with the Add Geometry Attributes tool (cf. Exercise 1 Step 3)

Spatial Reference: GCS_WGS_1984

Leave the other options as they are.

Exercise #2: Step 1 (cont.)

Copy Features

Input Features: tribalmap_Layer

• The output from Make XY Event Layer:
• Use the drop down menu

Output Feature Class: ...\temporary\ethno_centroids.shp

Exercise #2 (cont.)

Now save and run the Model.

Browse the output and its attribute table.

Is everything as expected?

Exercise #2: Step 2

Spatial Join

Target Feature Class: ethno_centroids.shp

• The output from Copy Features

Join Features: fishnet.shp

• The output from Add Geometry Attributes (in Exercise 1)

Output Feature Class: ...\temporary\ethno_centroids_with_20cr2.shp

Spatial Join (cont.)

Join Operation: JOIN_ONE_TO_ONE

• We match each ethnic group with one weather data cell

Check "Keep All Target Features"

• We want to know which ethnic groups aren't matched with weather data, if any

Field Map of Join Features: leave as it is

Match Option: INTERSECT

• Each ethnic group's centroid should match with the weather cell that intersects it

Exercise #2 (we're done!)

Now save and run the Model.

• I deliberately repeat this slide so you will form the habit of saving the Model before running it.

Browse the output and its attribute table.

Is everything as expected?

Export to Stata

Now we want to export the attribute table of ethno_centroids_with_20cr2.shp to Stata

• Then we can merge Ethnographic Atlas data with 20th Century Reanalysis data

3 ways to export the attribute table to the format readable by Stata

• Table To Excel
• Export Feature Attribute to ASCII
• shp2dta (a STATA ado)

Export to Stata (cont.)

Table To Excel

Converts the attribute table into an Excel file

Then use import excel in Stata

But Excel cannot handle more than 65535 rows...

Export to Stata (cont.)

Export Feature Attribute to ASCII

Converts the attribute table into an ASCII text file

Then use import delimited in Stata

This tool will automatically add centroid coordinates to the output ASCII file

Unlike Table To Excel, must specify which fields to export

Export to Stata (cont.)

shp2dta

This Stata ado directly reads a shapefile's attribute table

But it works only with polygons

Exercise #3

Export Attribute Table

1. Table To Excel

• Input Table (use drop-down menu): ethno_centroids_with_20cr2.shp
• Output Excel File: ...\output\ethno_centroids_with_20cr2.xls

Exercise #3

Export Attribute Table (cont.)

2. Export Feature Attribute to ASCII

• Input Feature Class (use drop-down menu): ethno_centroids_with_20cr2.shp
• Value Field: NAME, TRIBE_CODE, CENTROID_X, CENTROID_Y
• Delimiter: SPACE
• Not COMMA, to avoid confusing with decimal mark
• Output ASCII File: ...\output\ethno_centroids_with_20cr2.txt
• Check "Add Field Name to Output"

Exercise #3 (cont.)

Browse the exported tables

ethno_centroids_with_20cr2.txt has two additional columns

• XCoord: longitude
• YCoord: latitude

Export Feature Attribute to ASCII is preferrable for

• Controling which fields to be exported (ArcGIS tends to create tons of garbage fields)
• Dealing with 65535+ observations

But Table To Excel is simpler to execute

"Model" model for Lecture 2

Look at lec2model.tbx/exercises1-3 in the downloaded data folder solutions4exercises

Why Python?

Essential for replication

Convenient to repeat the same geo-processing

• When you obtain the updated version of input datasets
• When you change a process in the upstream
• Within a script by using a loop (Lectures 6 and 8)

How to write a Python script for ArcGIS?

Use Model Builder to write a draft script

Then edit the draft script

Throughout the course, we will learn various scripting tips

Exercise #4

Export Python script from Model Builder

1. If the model is not opened yet, right-click the model in Catalogue Window and click "Edit"

2. Click in the menu bar "Model > Export > To Python Script"

3. Save as ***.py

• Today, let's name it lecture2.py and save it in .../Desktop/Lecture2/code/

How to edit Python scripts

Use Python's default editor IDLE

• To run the script, you just need to press F5

Or use your favourite text editor

• I recommend Atom, with the Script package

Exercise #5.1

Use Python IDLE

1. Click the Windows icon at the bottom-left

2. Click ArcGIS > IDLE (Python GUI)

3. Click File > Open to read a script

Exercise #5.2

Use Atom

1. Click the Atom icon (either on Desktop or Taskbar)

2. Click File > Add Project Folder... and choose ...Desktop\Lecture2

• This shows sub-directories inside the Lecture2/ folder
• No need to go back and forth with File Explorer

3. Click code > lecture2.py to read a script

How to edit Python scripts (cont.)

Have your own template script for executing ArcGIS geo-processing tools

Then copy-and-paste command lines from the exported script to your template

• This saves time
• Also avoid error making

For this lecture, I've prepared the template script (.../Lecture2/code/template4L2.py)

How to edit Python scripts (cont.)

Using this template script, we now learn the basics of Python scripting for ArcGIS

cf. To learn Python, visit Codecademy (free of charge)

Python Essentials for ArcGIS

1. Object, Property, Method

2. Try-Except statement

3. String variables

4. Print

5. Comments

Python Essentials for ArcGIS #1.1

Object

An object is a set of commands

• arcpy is an object containing all the ArcGIS geoprocessing tools

The import command reads this object (i.e. launch ArcGIS)

Object (cont.)

An object may contain smaller objects

• arcpy.env is an object contained in arcpy

Two types of commands in an object: property and method

Python Essentials for ArcGIS #1.2

Property

Contains a value (numbers, strings, True/False)

To assign a new value of the property, type:

object.property = value

• overwriteOutput: whether the overwriting of output files is allowed
• workspace: working directory name

Overwriting output files

By default, overwriting the output file is not allowed.

• Run a script. Browse the output. You're not satisfied. Revise the script. Run the script again.
• You'll then get an error.

The following command line (case-sensitive!)

arcpy.env.overwriteOutput = True

allows you to overwrite output files.

• Note: Python is case-sensitive

Directory Name in Python

arcpy.env.workspace = "D:/temp"

Never use \

• In Python, \ is used for line continuation
• In Windows, \ is used for directory path

Use / or \\

• The script exported from Model Builder uses \\

Python Essentials for ArcGIS #1.3

Method

is a function (i.e. transform inputs into outputs)

e.g. Geo-processing tool in ArcGIS: methods of the arcpy object

To use a method, type:

object.method(arg1, arg2, ...)

Exported Python script

Why we use Model Builder

The arcpy method names mix uppercase and lowercase letters as well as underscores

Arguments for these methods are often very long with lots of [ ] " ' ; , etc.

$\Rightarrow$ Better to first use Model Builder to export the draft script (until you get used to Python programming)

Online Help for Arcpy Methods

Visit ArcGIS for Desktop website and type the method name in the search field at the top row

• There's a built-in help, too, but the web version is more often updated

• Once we're used to Python, we will learn how to read this help document

Python Essentials for ArcGIS

1. Object, Property, Method

2. Try-Except statement

3. String variables

4. Print

5. Comments

Python Essentials for ArcGIS #2

Try-Except statement

If you simply run commands and get an error, you won't get a message on what went wrong

Try-except statement is essential to know what the error is about

Try-Except statement (cont.)

Python first attempts to execute indented commands below try:

If there is no error:

Python skips all the indented commands after except:

If there is an error:

Python executes the indented commands below except:

$\Rightarrow$ Write commands for error messages after except:

Exercise #6

Use try-except statement

1. Copy the geoprocessing commands in the exported script

2. Paste them between try: and except: in the template script

3. Select commands to be indented

4. Click the tab key (Atom) or Format > Indent Region (IDLE)

You should have something like this:

						############################## Geoprocessing ##########################
try:
    # Process: Create Fishnet
    arcpy.CreateFishnet_management(fishnet_shp, "-21 -41", "-21 -10", "2", "2", "41", "41", "", "NO_LABELS", "DEFAULT", "POLYGON")

    # Process: Make XY Event Layer
    arcpy.MakeXYEventLayer_management(tribalmap_shp, "lon", "lat", tribalmap_Layer, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]];-400 -400 1000000000;-100000 10000;-100000 10000;8.98315284119522E-09;0.001;0.001;IsHighPrecision", "")

    # Process: Copy Features
    arcpy.CopyFeatures_management(tribalmap_Layer, ethno_centroids_shp, "", "0", "0", "0")

    # Process: Define Projection
    arcpy.DefineProjection_management(fishnet_shp, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]]")

    # Process: Add Geometry Attributes
    arcpy.AddGeometryAttributes_management(fishnet_shp__2_, "CENTROID", "", "", "")

    # Process: Spatial Join
    arcpy.SpatialJoin_analysis(ethno_centroids_shp, fishnet_shp__4_, ethno_centroid_with_20cr_shp, "JOIN_ONE_TO_ONE", "KEEP_ALL", "", "INTERSECT", "", "")

    # Process: Table To Excel
    arcpy.TableToExcel_conversion(ethno_centroid_with_20cr_shp, ethno_centroid_with_20cr_xls, "NAME", "CODE")

    # Process: Export Feature Attribute to ASCII
    arcpy.ExportXYv_stats(ethno_centroid_with_20cr_shp, "CENTROID_X;CENTROID_Y;NAME;TRIBE_CODE", "SPACE", ethno_centroid_with_20cr_txt, "ADD_FIELD_NAMES")

# Return geoprocessing specific errors
except arcpy.ExecuteError:
    print arcpy.GetMessages()
					

Python Essentials for ArcGIS

1. Object, Property, Method

2. Try-Except statement

3. String variables

4. Print

5. Comments

Python Essentials for ArcGIS #3

String variables

It's similar to local macro in Stata

To create a variable called file1 which contains a string data.shp, type

file1 = "data.shp"

• Don't forget to enclose the file name with double quotation marks

String variables (cont.)

Recommended to assign a string variable to each data file name in the Python script

• You may later want to use a different input file for the same data processing
• Then you just need to change one line in the script where the input file name is defined

Exercise #7

Edit file names

1. Copy local variables in the exported script

2. Paste them before try: in the template script

3. Sort these names by inputs, intermediates, and outputs

4. Assign the directory path for outputs to arcpy.env.workspace

5. Delete the directory path for outputs and intermediates

Exercise #7 (cont.)

Now notice

This happens when we use overwriting geoprocessing tools (Define Projection, Add Geometry Attributes)

It's confusing. So:

6. Press ctrl + f (or click Edit > Replace for IDLE) to replace:

• fishnet_shp__2_ with fishnet_shp
• fishnet_shp__4_ with fishnet_shp

7. Delete the duplicated lines

You should now have something like this:

						import arcpy

### Set environment ###
# Allow the overwriting of the output files
arcpy.env.overwriteOutput = True # This command is CASE-SENSITIVE
# Set the working directory.
arcpy.env.workspace = "C:\\Users\\your_username\\Desktop\\Lecture2" # NEVER USE single backslash (\).

### Local variables ###
tribalmap_shp = "input\\tribalmap.shp"

tribalmap_Layer = "tribalmap_Layer"
ethno_centroids_shp = "temporary\\ethno_centroids.shp"
fishnet_shp = "temporary\\fishnet.shp"
ethno_centroid_with_20cr_shp = "temporary\\ethno_centroid_with_20cr.shp"

ethno_centroid_with_20cr_xls = "output\\ethno_centroid_with_20cr.xls"
ethno_centroid_with_20cr_txt = "output\\ethno_centroid_with_20cr.txt"

############################## Geoprocessing ##########################
try:
    # Process: Create Fishnet
					

Python Essentials for ArcGIS

1. Object, Property, Method

2. Try-Except statement

3. String variables

4. Print

5. Comments

Python Essentials for ArcGIS #4

Print

It's a Python's equivalent of display in Stata

To show a message on the IDLE screen while running the script, type:

print "message"

• Tells which part of the script is currently run
• Lets you know where the script caused an error
• Can be used to display a value that a method returns

print arcpy.GetMessages()

Exercise #8

Add print commands

For each geo-processing step, add the print command to explain what's being processsed.

Also add the print commands at the beginning of the script

You should now have something like this:

						############################## Preamble #################################
print "Launch ArcGIS"
import arcpy

### Set environment ###
print "Enable the overwriting"
arcpy.env.overwriteOutput = True # This command is CASE-SENSITIVE
print "Set the working directory"
arcpy.env.workspace = "C:\\Users\\Masayuki Kudamatsu\\Desktop\\Lecture2" # NEVER USE single backslash (\).

### Local variables ###
print "Input file names being set"
tribalmap_shp = "input\\tribalmap.shp"

print "Intermediate file names being set"
tribalmap_Layer = "tribalmap_Layer"
ethno_centroids_shp = "temporary\\ethno_centroids.shp"
fishnet_shp = "temporary\\fishnet.shp"
ethno_centroid_with_20cr_shp = "temporary\\ethno_centroid_with_20cr.shp"

print "Output files being set"
ethno_centroid_with_20cr_xls = "output\\ethno_centroid_with_20cr.xls"
ethno_centroid_with_20cr_txt = "output\\ethno_centroid_with_20cr.txt"
					

You should now have something like this (cont.):

						############################## Geoprocessing ##########################
try:
    print "Create 20th Century Reanalysis data cell polygons step 1/3"
    arcpy.CreateFishnet_management(fishnet_shp, "-21 -41", "-21 -10", "2", "2", "41", "41", "", "NO_LABELS", "DEFAULT", "POLYGON")

    print "Create 20th Century Reanalysis data cell polygons step 2/3"
    arcpy.DefineProjection_management(fishnet_shp, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]]")

    print "Create 20th Century Reanalysis data cell polygons step 3/3"
    arcpy.AddGeometryAttributes_management(fishnet_shp, "CENTROID", "", "", "")

    print "Create ethnic group centroids step 1/2"
    arcpy.MakeXYEventLayer_management(tribalmap_shp, "lon", "lat", tribalmap_Layer, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]];-400 -400 1000000000;-100000 10000;-100000 10000;8.98315284119522E-09;0.001;0.001;IsHighPrecision", "")

    print "Create ethnic group centroids step 2/2"
    arcpy.CopyFeatures_management(tribalmap_Layer, ethno_centroids_shp, "", "0", "0", "0")

    print "Match Ethnographic Atlas ethnic groups with 20th Century Reanalysis data cells"
    arcpy.SpatialJoin_analysis(ethno_centroids_shp, fishnet_shp, ethno_centroid_with_20cr_shp, "JOIN_ONE_TO_ONE", "KEEP_ALL", "", "INTERSECT", "", "")

    print "Export output data as Excel sheet"
    arcpy.TableToExcel_conversion(ethno_centroid_with_20cr_shp, ethno_centroid_with_20cr_xls, "NAME", "CODE")

    print "Export output data as csv file"
    arcpy.ExportXYv_stats(ethno_centroid_with_20cr_shp, "CENTROID_X;CENTROID_Y;NAME;TRIBE_CODE", "SPACE", ethno_centroid_with_20cr_txt, "ADD_FIELD_NAMES")

# Return geoprocessing specific errors
except arcpy.ExecuteError:
					

Python Essentials for ArcGIS

1. Object, Property, Method

2. Try-Except statement

3. String variables

4. Print

5. Comments

Python Essentials for ArcGIS #5

Comments

To insert comments, type # at the beginning of a comment

Useful for others to understand (and for you to remember) what each command does

Also useful if you want to skip some commands for the time being

Exercise #9

Skip command lines temporarily

Suppose you're not sure if this script will properly create ethnic group centroids.

So you want to temporarily skip the other parts of the script

1. Select command lines to be skipped

• Don't select the except: part

2. Press ctrl + /

• for IDLE, click Format > Comment Out Region

$\Rightarrow$ # will appear at the beginning of selected commands

You should have something like this:

						############################## Geoprocessing ##########################
try:
#    print "Create 20th Century Reanalysis data cell polygons step 1/3"
#    arcpy.CreateFishnet_management(fishnet_shp, "-21 -41", "-21 -10", "2", "2", "41", "41", "", "NO_LABELS", "DEFAULT", "POLYGON")
#
#    print "Create 20th Century Reanalysis data cell polygons step 2/3"
#    arcpy.DefineProjection_management(fishnet_shp, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]]")
#
#    print "Create 20th Century Reanalysis data cell polygons step 3/3"
#    arcpy.AddGeometryAttributes_management(fishnet_shp, "CENTROID", "", "", "")

    arcpy.MakeXYEventLayer_management(tribalmap_shp, "lon", "lat", tribalmap_Layer, "GEOGCS['GCS_WGS_1984',DATUM['D_WGS_1984',SPHEROID['WGS_1984',6378137.0,298.257223563]],PRIMEM['Greenwich',0.0],UNIT['Degree',0.0174532925199433]];-400 -400 1000000000;-100000 10000;-100000 10000;8.98315284119522E-09;0.001;0.001;IsHighPrecision", "")
    print "Create ethnic group centroids step 1/2"

    print "Create ethnic group centroids step 2/2"
    arcpy.CopyFeatures_management(tribalmap_Layer, ethno_centroids_shp, "", "0", "0", "0")

#    print "Match Ethnographic Atlas ethnic groups with 20th Century Reanalysis data cells"
#    arcpy.SpatialJoin_analysis(ethno_centroids_shp, fishnet_shp, ethno_centroid_with_20cr_shp, "JOIN_ONE_TO_ONE", "KEEP_ALL", "", "INTERSECT", "", "")
#
#    print "Export output data as Excel sheet"
#    arcpy.TableToExcel_conversion(ethno_centroid_with_20cr_shp, ethno_centroid_with_20cr_xls, "NAME", "CODE")
#
#    print "Export output data as csv file"
#    arcpy.ExportXYv_stats(ethno_centroid_with_20cr_shp, "CENTROID_X;CENTROID_Y;NAME;TRIBE_CODE", "SPACE", ethno_centroid_with_20cr_txt, "ADD_FIELD_NAMES")

# Return geoprocessing specific errors
except arcpy.ExecuteError:
					

Exercise #9 (cont.)

3. Save and run the script

• The Script package of Atom lets you run the script by pressing ctrl + shift + b
• For IDLE, press F5

4. Cross your fingers :-)

5. Check if ethno_centroids.shp is created properly.

• Don't forget Refresh if you don't see it

Exercise #9 (cont.)

6. Now uncomment those skipped commands

• Select the commented-out lines and press ctrl + /
• For IDLE, click Format > Uncomment Region

7. Save and run the entire script

• The Script package of Atom lets you run the script by pressing ctrl + shift + b
• For IDLE, press F5

8. Cross your fingers :-)

9. Check if everything is as expected

Exercise #9 (cont.)

Most likely, you get an error message:

ERROR 000464: Cannot get exclusive schema lock. Either being edited or in use by another application.

This error occurs when the script is trying to overwrite the output that's been shown in ArcMap

Before you run the Python script, always close all the output files in ArcMap

Error handling

Sometimes, the output file is not what you intended.

e.g., New fields in the attribute table are all zero

Revising the script may not solve the issue / You cannot find anything wrong with the script

If so, reboot ArcMap/IDLE and even Windows. This often solves the issue.

Still unsolved, ask Google.

• Someone else may have had the same problem and posted the question on the web
• And ArcGIS experts may have answered the question

Last resort: ask at Stack Exchange or ArcGIS Forum.

Model Python Script for Lecture 2

Look at

solutions4exercises/lec2script.py

in the downloaded data folder for Lecture 2