Putting Together a Network of Linear GIS Features: Gathering Linear Features, Building Topology, and Attributing (Especially for GATE-Geospatial 2022)

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Here we use the example from Moscow, Idaho. A university town of 25,000 people, Moscow, Idaho, has the same network features as other larger cities except for overpasses or underpasses. Putting together a network involves three tasks:

Diagram Shows a Network Involves Three Tasks

1. Gathering Linear Features

Gathering linear features are from a network data source. The TIGER/Line files from the U. S. Census Bureau are a common data source for making preliminary street networks in the United States. They are free for download at the Census Bureau website. The TIGER/Line files are in shapefile format and measured in longitude and latitude values based on NAD83. Road network data can also be digitized or purchased from commercial companies.

2. Building Topology

A network converted from the TIGER/Line files has the built-in topology: the streets are connected at nodes are designated as either from-nodes or to-nodes. If topology is not available in a data set, one can use a GIS package to build the topology. ArcGIS, for example, can build network topology using a shapefile or a geodatabase.

Editing and updating the road network is the next step. When superimposing the road network over Orthophotos or high-resolution satellite images, one may find that the street centerlines from the TIGER/Line files deviate from the streets. Such mistakes must be corrected. Also, new streets must be added. In some cases, pseudo nodes must be removed so that a street segment between two intersections is not unnecessarily broken up.

3. Attributing the Network Features

Network attributes in this example include the link impedance, one-way streets, speed limits, and turns. The link impedance value can be the physical distance or the travel time. They physical distance is the length of a street segment. The travel time can be derived from the length and the speed limit of a street segment. Roads converted from the TIGER/Line files have the field MTFCC, classifying roads as primary road, secondary road, and so on, which can be used to assign speed limits.

Table Shows Possible Turns at Node 341

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