Python & Drive Time Analyses

Python 2.6ArcCatalog 9.3.1ArcMap 9.3.1

Project technologiesProgramming language:

Software products:

Janice PoehlmanDivision of Forestry, Dept. Natural Resourcesjanice.poehlman@wisconsin.gov

Use python scripts to summarize the total number of people who are

within drive times of a location.

30 Minute60 Minute90 Minute

120 Minute

Drive Time Service AreaNetwork Analyst}

Data

WI, MN, MI, IL, IA

• Census 2000

Block Groups

• TIGER 2000 Road

• PLSS Township

#---------------------------------------------------------------------#Author: JP ##Last Update: December, 2010##Purpose: #Use cursors to select individual records (rows) in feature class. The#individual record is saved to an individual feature class and used to#clip census block groups. A town-range field is added and calculated#for each census block group feature class. The block group individual#files are merged into a single feature class, which can be summarized#by DTR for total population for each drive time service area.#-----------------------------------------------------------------------

What is a cursor and how does it work.

What is a cursor and how does it work.

What is a cursor and how does it work.

What is a cursor and how does it work.

What is a cursor and how does it work.

1.The cursor selects an individual record in a feature class and uses the python

tool to create a new feature class with one feature. (data export selected set):

gp.SearchCursor

What the python script does inside the cursor with one record:

2. Creates a new feature class from the record

gp.Select_Analysis

3. Clips block groups by the new feature class

gp.Clip_Analysis

4. Calculates a total population for the service area

gp.Calculate_Field 40417

#import modulesimport arcgisscripting, sys, os, time

#create the geoproccessor object and set file overwritegp = arcgisscripting.create()gp.overwriteoutput = 1

#set workspace variables and add toolboxesgp.workspace = "D:\drivetime\RoadsTigerResultsDT120Min_processing4.gdb”gp.addtoolbox("C:/Program Files/ArcGIS/ArcToolBox/Toolboxes/Data

Management Tools.tbx")gp.addtoolbox("C:/Program Files/ArcGIS/ArcToolBox/Toolboxes/Analysis

Tools.tbx")servicearea = "DriveTime120Minutes_SEW_NN”

log = open('D:/drivetime/logprocessing.log', 'a’)log.write('\n\nFile is ' + servicearea)timestamp = time.strftime('%I:%M:%S %p', time.localtime())log.write('\nStarting time is ' + timestamp)

What the python script does inside the cursor with one record:

2. Creates a new feature class from the record

gp.Select_Analysis

3. Clips block groups by the new feature class

gp.Clip_Analysis

4. Calculates a total population for the service area

gp.Calculate_Field 40417

try:

rows = gp.SearchCursor(servicearea)

row = rows.Next()

while row <> None:

ShapeName = str(row.DTR)

gp.Select_analysis(servicearea, "xxsel" +ShapeName, '"DTR"=' +ShapeName)

gp.clip_analysis("pop2000", "xxsel"+ShapeName, "xxclipSEWNN"+ShapeName, "") gp.calculatefield_management("xxclipSEWNN"+ShapeName, "DTR", row.DTR)

gp.delete_management ("xxsel" +ShapeName)

row = rows.next()

del row, rows

except:

if not gp.getmessages() == "”:

gp.addmessage(gp.getmessages(2))

if 'row' in dir():

del row

if 'rows' in dir():

del rows

After the cursor is used for geoprocessing every record, the individual feature classes containing block groups for each service area are merged together using a value table. gp.merge_management

vTab = gp.createobject("ValueTable”)fcList = gp.listfeatureclasses("xxclipSEWNN*”)fc = fcList.Next()while fc: fcpath = gp.workspace + "\\" + fc vTab.Addrow(fcpath) fc = fcList.Next()gp.merge_management(vTab, "AMergedDriveTime120MinutesSEWNN", "”)print "Completed merged file for features of %s" %(servicearea)timestamp = time.strftime('%I:%M:%S %p', time.localtime())log.write('\nFinishing time is ' + timestamp)print"Done.”del vTabdel fcdel fcpathdel serviceareadel timestamplog.close()

A supply and demand analysis oflocation to people.

•Using hunting or fishing licensing information to determine if quality or quantity of lands support types of recreation.•Using the density of people to determine where to build facilities or infrastructure.

Voila!

Thank you for your attention.