1. Geography 465 GIS Database Programming
Getting Started with GIS Database Programming

2. See Geog 465 course web site for Overview and Schedule

3. What is GIS Database Programming?
Geoprocessing - application of GIS operations on a set of data inputs for generating information.
Database (DB) programming – the part of geoprocessing focusing on DB manipulation; not quite spatial analysis but almost.
Use scripting to automate DB programming

4. Why write scripts?
Scripts supply the added benefit of decision making logic and looping functionality
Automate a work flow, for example:
Copy all incoming data into a geodatabase
Perform a project, clip, buffer operation on multiple data sets (iterate)
Easily distribute code
A script is a self-contained, single file

5. Why use Python for Scripting?
An open-source, object-oriented, scripting language
Offers IDE (integrated development environment) with debugging tools
Modular, can be broken apart
Ability to compile scripts
Installed with ArcGIS 9 and ESRI samples provided

6. Writing code in Python Writing Python code
Python command line
IDE (integrated development environment) e.g., PythonWin and Komodo
Michalis will use Komodo Edit (open source editor - free)
IDE allows you to perform all jobs from one location
Write, Save, Run, and Debug code

7. PythonWin Interface Script window Interactive window
Write and save code
Interactive window
Test lines of code
Report messages
Menus and Toolbars
standard and debugging

8. Basics of Python Comment: A non-executable line of code
One number sign (#) for green and italicized
Two number signs (##) for gray
# Name: Michalis Avraam
# Date: January 5, 2009
# Purpose: To buffer a feature class
import win32com.client
gp = win32com.client.Dispatch(“esriGeoprocessing.GpDispatch.1”)
## gp.Workspace = “C:\\Python_Data\\SanDiego.mdb”
Gp.Buffer_analysis (“Freeways”, “BuffFreeway”, 1000)
Can comment and uncomment blocks of code

9. Creating Scripts in Python
Use of ArcGIS help system to find:
Usage, command syntax, and scripting examples of standard ArcToolbox tools,
Usage and syntax of Geoprocessor properties and methods, which are only accessible through scripting

10. Running Python Scripts Three Modes
1) Running scripts in IDE, e.g. PythonWin
2) Running scripts as script tools in ArcGIS
3) Running scripts as embedded model components in ArcGIS

11. (non) Running Scripts in Python
Problem with the schema lock
Cannot manipulate with the same file open in ArcGIS and in IDE at the same time

12. Running scripts in PythonWin
Example of a simple script to buffer a feature class
# Name: Tim Nyerges
# Date: January 5, 2009
# Purpose: To buffer a feature class
import win32com.client
gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1“
gp.Workspace = "C:\\Python_Data\\SanDiego.mdb”
gp.Buffer_analysis ("Freeways", "BufferedFreeways", 1000)

13. Debugging the Code Test code in Python Win (or other IDE)
A check for syntax errors
Do not test a script from ArcToolbox
Test code in PythonWin, then add it to ArcToolbox

14. Running scripts in PythonWin
Run the script from the script window of PythonWin
Check the message in the lower left corner of the interactive window in PythonWin:
While the script is running you will see the message
“running script <….>.py”
The indication of the successful run is the message
“Script <….> returned the exit code 0”
Display the result in ArcCatalog

15. Running scripts in PythonWin
Example of a simple script to clip a feature class
# Name: Tim Nyerges
# Date: January 3, 2007
# Purpose: To clip a feature class
import win32com.client
gp =win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
gp.Workspace = "C:\\Python_Data\\SanDiego.mdb"
gp.Clip_analysis ("MajorAttractions", "SDdowntown", "SDdowntownAttractions")

16. Running scripts in PythonWin
Example of a simple script to buffer and clip a feature class
# Name Tim Nyerges
# Date: January 5, 2009
# Purpose: To buffer SD freeways first and then to clip the downtown section
# of freeways
import win32com.client
gp = win32com.client.Dispatch("esriGeoprocessing.GpDispatch.1")
gp.Workspace = "C:\\Python_Data\\SanDiego.mdb"
if gp.Exists(gp.Workspace + "\\bufferedFreeways"):
gp.Delete_management(gp.Workspace + "\\bufferedFreeways")
gp.Buffer_analysis ("Freeways", "bufferedFreeways", "500")
gp.Clip_analysis ("bufferedFreeways", "SDdowntown", "downtownFreeways")

17. Michalis will get you started in labb session… “hands-on” Python and Komodo edit

18. Two different variables
Variables in Python
Variables are dynamically typed
No declaration required
No type assignment required
fc = “C:\\ProjectData\\SanDiego.mdb\\Freeways.shp”
Variables are case sensitive
fc = “Freeways.shp”
Fc = 20000
Variables can hold different data types
numbers, strings, lists, files
Two different variables

19. Numbers Variables can hold numbers and expressions num1 = 1.2

20. Strings Variables can hold strings folder = “c:/Student”
Strings are surrounded in double (“) or single (‘) quotes
Pathnames use two back (\\) or one forward (/) slash
One backslash (\) is a reserved escape character and a line continuation character

21. Strings Strings can be combined together gdbPath = “c:\\SanDiego.mdb”
fc = “Roads”
fullPath = gdbPath + “\\” + fc
Strings are indexed
strings are zero-based from the left and one-based from the right
fc = “Streets.shp”
fc[0] ---> “S” # S is in the 0 position
fc[1:3] ---> “tr” # start at 1st, up to not including 3rd
fc[:-4] ---> “Streets” # get rid of the last 4 charaters
C:\SanDiego.mdb\Roads”

22. Lists Variables can hold lists Lists are indexed numList = [1, 2, 3]
fcList = [“Roads”, “Streets”, “Parcels”, “Zipcodes”]
Lists are indexed
fc1 = fcList[1]
fc2 = fcList[0:2] > “Roads”, “Streets”
fc3 = fcList[0:-1] > “Roads”, “Streets”, “Parcels”
fc4 = fcList[2:] > “Parcels”, “Zipcodes”
---> “Streets”

23. Variable naming conventions
Upper case versus lower case
First word lower case, capitalize each successive word
tableFieldName = “Street”
- Acronym at the beginning, use lower case letters
gdbPath = “C:\\SanDiego.mdb”
Acronym in the middle or at the end, use upper case letters
inputFC = “Streets.shp”
Avoid special characters (for example / \ & % # !)
Use descriptive variable names

24. Line continuation Line continuation characters
Parentheses ( ), brackets [ ], and braces { }
Backslash \
Indentation is automatic
fcList = [“Roads”, “Climate”, “Streams”,
“Zipcodes”, “Coastlines”]
distanceValues = 100, 200, 300, 400, 500, \
1000, 1500
gp.Buffer_analysis(fcList[2], BuffStreams1000, distanceValues[5])