Department of Geography and Urban Studies, Temple University

GUS 0265/0465Applications in GIS/Geographic

Data Analysis

Lecture 4: Network Operations

Features of a Road Network

Link Impedance: weights on an link

Turn Impedance: time it takes to complete a turn at a given node

Turn Table: table listing turn options and impedance for each node

One way or closed streets

Overpasses and Underpasses

Road Network Operations

Address Geocoding

Shortest Path Analysis

Closest Facility

Allocation

Location-Allocation

Road Network Operations

Address Geocoding

Takes an address in text form and assigns it a geographic coordinate location

Address GeocodingLeft_from Left_to Right_from Right_to Street_name Type Left_Zone Right_Zone201 299 200 298 SUNSET ST 92374 92373

209 Sunset St.

209 House numberSunset Street nameSt. Type92374 Zone

Road Network Operations

Shortest Path Analysis

Finding the shortest path (in travel cost, not just distance) between two locations on the network.

Djikstra’s Algorithm….

http://www.unf.edu/~wkloster/foundations/DijkstraApplet/DijkstraApplet.htm

Shortest Path Analysis

Traveling salesman problem:

Given a number of stops, find the shortest route that begins at a given location and ends at the same location.

http://riot.ieor.berkeley.edu/~cander/cs270/

Road Network Operations

Closest Facility

Finds the closest facility to a given location on a network. Essentially, a multiple shortest path analysis among the given location and each in a set of candidate facilities. The facility with the shortest path is the closest.

Road Network Operations

Allocation

Allocating a region in space to a point facility. For example, allocating urban areas to fire districts based on proximity to the nearest fire station. Each station is allocated a given area.

Allocation

Shaded area indicates areas within 2 minutes of a fire station

Road Network Operations

Location-Allocation

Finding a location for a point location on a network to maximize some allocation criteria. For example, given the criteria that all areas must be within 2 minutes of a fire station, where should another fire station be built?

Road Network

Operations

Road Network

Operations

Allocation

Road Network

Operations

Location-Allocation

Road Network Operations

Location-Allocation

Minimum distance model – minimizes the total distance traveled from all demand points to their nearest supply centers

Maximum covering model – maximizes the demand covered within a specified time or distance

Dynamic Segmentation

allows for the representation of routes along a network.

was developed to store important network locations that are georeferenced based on their distance along the route from some starting point.

For instance, many transportation agencies store geographic information that is georeferenced to mileposts along a highway.

Dynamic Segmentation

Tables:

Route Table: each record is an individual route (a path along the network) with links to individual sections

Section Table: each record is an individual section linking a route to its component links

Event Table: each record is a ‘thing’ that exists along the route, e.g. a stretch of pavement quality, a bridge location, etc.

Arc Attribute Table: each record is an arc (table automatically generated by Arc/Info for vector topologic data structure)

Dynamic SegmentationRoute table

Section table

Roads AAT

Dynamic Segmentation

Dynamic Segmentation