Using Python with ArcGIS

Using Python with ArcGIS
Drew Flater, Nobbir Ahmed
Offering 184

Agenda
Python essentials
Arcpy, functions & classes
Script geoprocessing workflows
Automate map management & production
Customize Desktop with Python Add-ins
Analyze rasters with map algebra
Extend ArcGIS with Python

Python Essentials
Getting started with Python
in ArcGIS

What is Python?
“Python is an easy to learn, powerful language…
(with) high-level data structures and a simple but
effective approach to object-oriented
programming. Python’s elegant syntax and
dynamic typing…make it an ideal language for
scripting…in many areas and on most platforms.”
–python.org
Scripting language of ArcGIS
Free, cross-platform, easy to learn, widely
useful, great community

Python 101
Where do I write Python code?
Python file is text with .py extension
Edit in IDE like PyScripter, Wing IDE
Logic for testing conditions
If, else statement
Operators like >,

ArcPy
Site package included with ArcGIS that enables interaction
with Python
The access point to 900+ geoprocessing tools
A package of functions, classes and modules
Helper functions that perform useful tasks and enable automation
(ListFeatureClasses, Describe, SearchCursor)
Classes that can be used to create complex objects
(SpatialReference, Geometry, FieldMap)
Modules that provide specialized functionality
(mapping, SpatialAnalyst, data access)
Enhancement of arcgisscripting module (pre-10.0)
Your old scripts will work

Why use Python and ArcGIS?
Automate repetitive tasks
Batch processing
Develop workflows that
leverage hundreds of tools
and functions
Add geoprocessing services
to your application
Customize Desktop apps with
a language Esri is committed
to support
Extend the capabilities of
ArcGIS

Script
Geoprocessing
Workflows
Calling geoprocessing tools
through ArcPy and stringing
them together

Geoprocessing and Python
import arcpy
Follow tool syntax
arcpy.toolname_toolboxalias()
Enter input and output parameters
How do I use a specific tool?
Tool help page
Copy as Python Snippet
help(arcpy.Buffer_analysis)
Use geoprocessing environments as
global parameters
Accessed from arcpy.env
Productivity / code cleanup tool
workspace, extent, cellsize, mask

Demo
Script
Geoprocessing
Workflows
Perform batch processing, and
string together multiple tools to
perform spatial analysis

Tips & Tricks
Use the result object of geoprocessing tools
Returned by all tools
Maintains messages, parameters, and outputs
result = arcpy.Buffer_analysis(…)
Write intermediate tool output to in_memory workspace
Automatic cleanup
Faster read-write

Automate Map
Management &
Production
Working with maps and layers
using arcpy.mapping

ArcPy Mapping module
arcpy.mapping
Module that contains functions and classes used to
automate mapping tasks
Manage map documents, layers, and data
Find and fix broken data sources
Update layer symbology across many maps
Export and print map documents
Automate map production / map series

ArcPy Mapping module
MapDocument object is essential
References .mxd on disk; has methods and properties
Needed to perform most mapping tasks
MapDocument as input to function
Functions called from MapDocument
md = arcpy.mapping.MapDocument("…/NtlParks.mxd")
# Set map document properties
md.description = "Map of National Parks"
# List layers in the map
mapLayers = arcpy.mapping.ListLayers(md)
# Fix Data Sources
md.replaceWorkspaces(…)
# Export the map to PDF
arcpy.mapping.ExportToPDF(md, "…/NtlParks.pdf")

Mapping module resources
Download sample tools

Demo
Automate Map
Management &
Production
Make a multi-page map book
using arcpy.mapping and data
driven pages

Customize ArcGIS
Desktop with
Python Add-ins
Run Python code in response to
button clicks and application
events

ArcGIS Desktop Add-ins
Add-in framework provided to customize and extend ArcGIS
Desktop applications
Easy to build, install and share
Secured through digital signing
Supports C#, VB.NET, Java, and Python
Python makes add-ins easier!
No dlls, compiling, or ArcObjects, and less code

Python Add-in Types
Button
Tool
Toolbar
Tool Pallet
Combo Box
Menu
Extension
Dockable windows are not supported
No custom UI support

Python Add-In Classes and Methods
Button
Tool
onClick()
onCircle(), onLine(), onRectangle()
onMouseDown(), onMouseDownMap()
Application Extension
startup()
newDocument(), openDocument(), closeDocument()
contentsChanged(), itemAdded(), itemDeleted()
Full documentation of all functions and classes

Python Add-In Wizard
Add-ins are built using the Python Add-in wizard
The wizard generates fully stubbed out add-in projects
including the config.xml, folders, and the Python script
Download the Python Wizard from arcgis.com
Extract the contents of the .zip
Launch the addin_assistant.exe from the bin folder

Demo
Customize ArcGIS
Desktop with
Python Add-ins
Python Add-in toolbar with
buttons to select and zoom to
next or previous feature

Analyze Rasters
with Map Algebra
Using arcpy.sa (Spatial Analyst)
to efficiently work with rasters

Spatial Analyst Module
from arcpy.sa import *
arcpy.CheckOutExtension("Spatial")
Includes all Spatial Analyst tools
Helper classes that can be used to support complex
parameter in scripting
Integrates Map Algebra into Python
Defines geographic analysis as algebraic expressions
Supports mathematical, relational, other operators
Output on the left-side
slopeRas = Slope("elevRas") * 100.0

Raster Class
Reference to raster on disk, created in two ways:
Returned output from arcpy.sa functions
Cast using arcpy.Raster() function
Necessary for map algebra expressions using operators
Temporary raster dataset that can be saved
Has properties and method
raster.minimum, raster.format, raster.extent
raster.save()
dem = arcpy.Raster("Elevation_Meters.tif"))
demFt = dem * 3.28
# Rescale elevation to 0 – 1 scale
rescale = (dem - dem.minimum)/(dem.maximum-dem.minimum)
rescale.save("Elevation_Rescale_0_1.tif")

Demo
Analyze Rasters
with Map Algebra
Use raster processing with
Python to perform probabilitybased
site suitability

Extend ArcGIS
with Python
Using Python to do stuff that's
not in the ArcGIS box

Python packages
ArcGIS includes several 3 rd -party Python packages and
modules
No separate install or config required, just import
NumPy Statistical computation, powerful array object
Matplotlib Data presentation and graphing
Xlrd, Xlwt Excel spreadsheet read/write (new at 10.2)
PyPI - official Python Package Index
Vast collection of 3 rd -party packages with easy browse/search
Windows binaries
UC-Irvine maintains unofficial package installs for Windows
"A simple approach for including 3 rd party Python libraries with your scripts"

NumPy
NumPy is useful for mathematical &
statistical computation
Feature, table, and raster data can be
converted to NumPy arrays
1 3
2 4
1 3
2 4
3
4
Numpy Array
To NumPy From ArcGIS To ArcGIS From NumPy
3
4
Raster
arcpy.da.FeatureClassToNumPyArray arcpy.da.NumPyArrayToFeatureClass
arcpy.da.TableToNumPyArray arcpy.da.NumPyArrayToTable
arcpy.RasterToNumPyArray arcpy.NumPyArrayToRaster

ArcGIS, Python, and Beyond
Use Python as a communication language between ArcGIS
and other APIs, packages, or applications
"Extend ArcGIS with R"
"Call a dll from a script tool using ctypes"
Python…
Retrieves and organizes parameters/arguments from ArcGIS
Converts data as needed (shapefiles, IMG, NetCDF, etc.)
Constructs strings and uses operating system or class for execution
After execution, applies symbology, coordinate system, and creates
reports

Demo
Extend ArcGIS
with 3 rd -Party
Python Libraries
ArcGIS and NumPy roundtrip
and using 3 rd -party packages

Resources
resources.ArcGIS.com
Python community
arcpy.wordpress.com
GIS Stack Exchange, Stack Overflow
Python References
Learning Python by Lutz
The Python Standard Library by
Example by Hellmann
Python Scripting for ArcGIS
by Esri press
diveintopython.org
python.org
Working with the ArcPy DA Module
Wed 1:00pm – Smoketree A-E
Creating Tools in a Python Toolbox
Wed 2:30pm – Mesquite GH
Creating Geoprocessing Services
Tue 1:00pm – Smoketree A-E
Python Scripting for Map Automation
Wed 1:00 pm – Mojave Learning Ctr
Developing Python Add-ins
Tue 4:00pm – Primrose A
Working with Raster Data Using Py
Thu 8:30am – Primrose A
Integrating Open Source Stats Pkgs
Tue 1:30pm – Demo Theater 1, Oasis 1
Offering 184