Do It Yourself! Building a network dataset from local agency data By Mike Price, Entrada/San Juan, Inc. Tutorials in recent issues of ArcUser magazine have showed how to create mapped time- and distance-based travel network models for emergency response applications. Building these models required carefully prepared agency or commercial street data that had been tuned for network modeling. Many local agencies build and maintain quality street datasets, often designed to support highly reliable geocoding. While these streets can be very current and have great positional accuracy, they are often not built to support time- and distance-based networking. However, in many cases, it is possible to modify these street datasets to support a network model. This exercise uses a street dataset for Redlands, California, where Esri is headquartered. The Redlands City GIS streets data was designed and is maintained for address geocoding. After inspecting the data, the exercise explores several methods for modifying a copy of the data for time-based networking. This exercise involves careful heads-up editing. The Redlands street data in the sample dataset has been modified only slightly so exercise tasks can be accomplished more quickly. It is very similar to the original Redlands street dataset. This article assumes a basic understanding of ArcGIS Desktop and the ArcGIS Network Analyst extension. To review modeling travel networks with ArcGIS Network Analyst and the concepts of distribution and concentration, please read and work the exercises published in the July–September 2007, October–December 2007, and Summer 2008 issues of ArcUser and available online at www.esri.com/arcuser. These articles provide background information on how emergency responders use time as a response measure. Getting Starting To obtain the sample dataset for this exercise, visit the ArcUser Online Web site at www.esri. com/arcuser and download redlands.zip. This file contains all the data necessary to perform this tutorial. Unzip this data archive near the root directory on your hard drive. In Windows Explorer, right-click on the Redlands folder; choose Properties; and on the General tab, make sure Read Only is unchecked. Open ArcCatalog and navigate to the Redlands folder. Preview the data in Geography and Table modes. Notice that the data is in California State Plane North American Datum of 1983 (NAD 83) Zone V and units are U.S. Survey Feet. Preview the Redlands01.mxd file to see the study area for the exercise. Locate and carefully inspect the streets shapefile. This geocoding dataset was created and maintained by the City of Redlands. To protect the original file, make a copy of streets_ in and rename it streets_nw. The copied file, streets_nw, will be used for this exercise. This exercise explores several methods for modifying street data for use in time-based network modeling. Adding Fields for Results While in ArcCatalog, add three attributes to support the network model. Preview the streets_nw attribute table. In the Catalog tree on the left, right-click on streets_nw, choose Properties, and click the Field tab. Notice that the lowermost (rightmost) field in the source table is ADDRCITY. The three new fields will support directional time and distance networking. 1. Click the first blank line in the Field Name column and name the first new field OneWay. Specify the data type as text and the field length as four characters. Click Apply. This field will be used to code travel direction for all one-way streets. 2. Click in the next blank name field and type "Length_Mi." Specify a Double format with a Precision of 12 and a Scale of 6. Click Apply.When the length of each street segment is calculated in decimal miles later in this lesson, this field will hold those results. These values will be used to calculate travel time for all segments. ArcUser Summer 2009 www.esri.com