Introduction to GIS modeling and Python

Overview

Welcome to http://assistance-en-sig.blogspot.com/. Over the next ten weeks you'll work through four lessons and a final project dealing with ArcGIS automation in Python. Each lesson will contain readings, examples, and projects. Since the lessons are two weeks long, you should plan between 20 - 24 hours of work to complete them, although this number may vary depending on your prior programming experience. See the Course Schedule section of this syllabus, below, for a schedule of the lessons and course projects.

As with GEOG 483 and GEOG 484, the lessons in this course are project-based with key concepts embedded within. However, because of the nature of computer programming, there is no way this course can follow the step-by-step instruction design of the previous courses. You will probably find the course to be more challenging than the others. For that reason, it is more important than ever that you stay on schedule and take advantage of the course message boards and private e-mail. It's quite likely that you will get stuck somewhere during the course, so before getting hopelessly frustrated, please seek help from me or your classmates!

I hope that by now that you have reviewed our Orientation and Syllabus for an important course site overview. Before we begin our first project, let me share some important information about the textbook and a related Esri course.

Textbook and readings

The textbook for this course is Python Scripting for ArcGIS by Paul A. Zandbergen. This book came out in 2012 and has been a hot item among Esri software users; I suggest you order your copy immediately in case of shortages or delays.

Back when Geog 485 was rewritten as a Python course, there was no textbook available that tied together ArcGIS and Python scripting. As you read through Zandbergen's book, you'll see material that closely parallels what is in the Geog 485 lessons. This isn't necessarily a bad thing; when you are learning a subject like programming, it can be helpful to have the same concept explained from two angles.

My advice about the readings is this: Read the material on the Geog 485 lesson pages first. If you feel like you have a good understanding from the lesson pages, you can skim through some of the more lengthy Zandbergen readings. If you struggled with understanding the lesson pages, you should pay close attention to the Zandbergen readings and try some of the related code snippets and exercises. I suggest you plan about 1 - 2 hours per week of reading if you are going to study the chapters in detail.

In all cases, you should get a copy of the textbook because it is a relevant and helpful reference.

Esri Virtual Campus Courses Using Python in ArcGIS Desktop 10

There is a free Esri Virtual Campus course, Using Python in ArcGIS Desktop 10, that introduces a lot of the same things you'll learn this quarter in Geog 485. The course consists of a one-hour recorded seminar and a walkthrough exercise. If you want to get a head start, or you feel you want some reinforcement of what we're learning from a different point of view, it would be worth your time to complete this Virtual Campus course.

All you need in order to access this course is an Esri Global Account, which you can create for free. You do not need to obtain an access code from Penn State.

The video moves very quickly and covers a range of concepts that we'll spend 10 weeks studying in depth, so don't worry if you don't understand it all immediately. You might find it helpful to watch the video again near the end of Geog 485 to review what you've learned.

Questions?

If you have any questions now or at any point during this week, please feel free to post them to the Lesson 1 Discussion Forum. (To access the forums, return to ANGEL via the ANGEL link in the Resources menu. Once in ANGEL, you can navigate to the Communicate tab and then scroll down to the Discussion Forums section.) While you are there, feel free to post your own responses if you, too, are able to help a classmate.

Now, let's begin Lesson 1.

• Lesson 1 checklist
• 1.1.1 The need for GIS automation
• 1.2.1 Exploring the toolbox
• 1.2.2 Environments for accessing tools
• 1.2.3 Running a tool from its GUI
• 1.2.4 Modeling with tools
• 1.3.1 Why learn ModelBuilder?
• 1.3.2 Opening and exploring ModelBuilder
• 1.3.3 Model parameters
• 1.3.4 Advanced geoprocessing and ModelBuilder concepts
• 1.4.1 Introducing Python using the Python window in ArcGIS
• 1.4.2 What is Python?
• 1.4.3 Installing Python and PythonWin
• 1.4.4 Exploring PythonWin
• 1.5.1 Working with variables
• 1.5.2 Objects and object-oriented programming
• 1.5.3 Classes
• 1.5.4 Inheritance
• 1.5.5 Python syntax
• 1.6.1 Introductory Python examples
• 1.6.2 Example: Printing the spatial reference of a feature class
• 1.6.3 Example: Performing map algebra on a raster
• 1.6.4 Example: Creating buffers
• 1.7.1 Making a script tool
• Lesson 1 Practice Exercises
• Project 1, Part I: Modeling precipitation zones in Nebraska
• Project 1, Part II: Creating contours for the Fox Lake DEM

1.2.1 Exploring the toolbox

The ArcGIS software that you use in this course contains hundreds of tools that you can use to manipulate and analyze GIS data. Back before ArcGIS had a graphical user interface (GUI), people would access these tools by typing commands. Nowadays, you can point and click your way through a whole hierarchy of toolboxes using ArcCatalog or the Catalog window in ArcMap.

Although you may have seen them before, let’s take a quick look at the toolboxes:

1. Open ArcMap.
2. If the Catalog window isn't visible, click the Windows menu, then click Catalog. (If you've used previous versions of ArcGIS, this is a new window at version 10 that allows you to have a lot of the ArcCatalog functionality available in ArcMap.) If you hover over or click the Catalog item on the right side of your screen, you can make the Catalog window appear. Optionally, you can "pin" it down so that it doesn't hide itself.
3. In the Catalog, expand the nodes Toolboxes > System Toolboxes and continue expanding the toolboxes of your choice until you see some of the available tools. Notice that they’re organized into toolboxes and toolsets. Sometimes it’s faster to use the Search window to find the tool you need instead of browsing this tree.
4. Let’s examine a tool. Expand Analysis Tools > Proximity > Buffer, and double-click the Buffer tool to open it.
   At this point, you’re looking at a dialog with many fields. Each geoprocessing tool has required inputs and outputs. Those are indicated by the green dots. They represent the minimum amount of information you need to supply in order to run a tool. For the Buffer tool, as inputs, you’re required to supply an input features location (the features that will be buffered) and a buffer distance. You’re also required to indicate an output feature class location (for the new buffered features).
   Many tools also have optional parameters. You can modify these if you want, but if you don’t supply them, the tool will still run using default values. For the Buffer tool, optional parameters are the Side Type, End Type, Dissolve Type, and Dissolve Fields. Optional parameters are typically specified after required parameters.
5. Click the Show Help button in the lower-right corner of the tool (if it says Hide Help then you’re already viewing help). You can now click on any parameter in the dialog to see an explanation of that parameter appear in the right-hand window.
   If you’re not sure what a parameter means, this is a good way to learn. For example, with the help still open, click the Side Type input box on the Buffer tool (right where it says "FULL"). The Help explains what the Side Type parameter means and lists the different options: FULL, LEFT, RIGHT, and OUTSIDE_ONLY.

If you need even more help, each tool is fully documented in the ArcGIS Desktop Help. You could go directly to the Buffer tool help by clicking the Tool Help button in the tool dialog box, but in this course you'll often want to get to these help pages without opening the tool itself. Below are the steps for doing so.

1. From the main menu of ArcMap, click Help > ArcGIS Desktop Help. Optionally, for the most up-to-date help, you can use the Web-based help at http://webhelp.esri.com. (All links to the Help in this course will open the Web Help.)
2. In the ArcGIS Desktop Help table of contents, expand Professional Library > Geoprocessing > Geoprocessing tool reference. (If you are using 10.1, browse to Geoprocessing > Tool Reference instead.) Notice that the help topics in this section are organized into toolboxes and toolsets, paralleling the layout of the ArcGIS System Toolboxes.
3. Continue navigating the help table of contents to Analysis toolbox > Proximity toolset > Buffer. Scroll through the entire topic examining all the information that is given about the Buffer tool. Here you get tips about what the Buffer tool does, how to use it, a full list of parameters, and scripting examples written in Python. These scripting examples will be extremely valuable to you as you complete the assignments in this course and you should always check the Geoprocessing Tool Reference in the Help if you’re having trouble getting a tool to run in Python.