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Geog406-Network Analysis

Lecture 3

Network Analysis

Geog406-Network Analysis

OutlineNetwork AnalysisGIS and Transportation PlanningLinear Reference SystemSteps in Route Analysis/Linear

Referencing

Geog406-Network Analysis

Network Analysis

Used to represent and analyze cost, time, delivery and accumulation of resources along networks.

Need for management/tools to use and maintain networks.

Common Networks:– Roads, powerlines,

telephone cables, etc…

Geog406-Network Analysis

Network Analysis

3 Common problems analyzed using networks:

Route SelectionResource/Territory AllocationTraffic Modeling

Geog406-Network Analysis

Network Analysis

Route Selection– Identify best route based on

a set of criteria.– Ex. Find the shortest,

quickest or least costly route.

– Traveling Salesman Problem: Least cost tour through a set of nodes so that each node is visited exactly once.

– The closest facilityThe nearest hospitalThe nearest school

Geog406-Network Analysis

Network Analysis

Resource Allocation– Distribution of networks to

centers.– Territories are assigned to

one or more allocation centers in a network.

– All routes pursued, not just least cost route.

– The service area: The areas within certain distance or time from facilities

– Ex. School districts may use resource allocation to assign neighborhoods to schools.

Geog406-Network Analysis

Network Analysis

Travel costs– Time– Distance– Restrictions: one-way streets, closed streets,

prohibited turns

Traffic Modeling– Streets represented by interconnected arcs and

nodes.– Attributes associated with arcs define travel speed

and direction.– Traffic is placed in network and movement modeled.

Geog406-Network Analysis

Applications of GIS in Transportation

Database– Roads, routes, stop signs, accidents,

pavement, construction

Routing– Which route is the best

Transportation Planning– Traffic prediction/modeling

Geog406-Network Analysis

Network Analysis

Centers– A set of connected features in a network– May be centers of demand, supply or both.

Network Links– Connect and provide paths between centers.

Transit Costs– “Price” of moving a resource through a segment of a network. i.e.

time, distance, monetary units using pathfinding algorithms.

Geog406-Network Analysis

Linear Referencing System

Defined: The method of storing geographic locations by using relative positions along a measured linear feature. Example: route I-10, Kilometer 23.

Geog406-Network Analysis

Linear Referencing Systems

Applications– Collecting data along linear features such

as roads, rivers, and railways– Managing pavement quality– Managing urban networks and inventories

such as street signs, traffic lights, pedestrian crossings, bicycle paths, curbs, and sidewalks

– Managing railroad track quality

Geog406-Network Analysis

Linear Referencing System

Reference systems– Geographic reference system– Grid referencing system– Non-coordinate reference system

– Locations are coded with a two dimensional X, Y coordinate system

– Examples: (10, 20), (103.5, 2.3)

Geog406-Network Analysis

Linear Referencing System

Geocoding: The process of assigning a location, usually in the form of coordinate values (points), to an address by comparing the descriptive location elements in the address to those present in the reference material.

Geog406-Network Analysis

Linear Reference System

A collection of routes can be stored in a feature classExample: a set of bus routes in a cityDynamic Segmentation: The process of computing the map locations of events stored and managed in an event table using a linear referencing measurement system and displaying them on a map.

Geog406-Network Analysis

Linear Reference System

Route:– A route is a linear feature

that has a unique identifier and measurement system stored with it

– Routes measurements are stored with its geometry

– (X, Y, M) – X, Y and M can be in

different measurement units

Geog406-Network Analysis

Route Location

A route location describes a portion of a route (line) or a discrete (point) location along a route.– A linear route location: From .. To…

Example: Mile 2 to mile 4 on the I-10

– A point location: a single measurementMile 4 along I- 405

Geog406-Network Analysis

Route Event Tables

Tables to store route locations and their attributesEvents tables are organized based on common theme– Speed limits– Year of surfacing– Present Condition– Signs– Accidents

Geog406-Network Analysis

Route Event Tables

At least two columns:– An event Key– Measure location(s)

Can be one column: location along the route where the event occurs

– Point Event Table

Or it can be two columns: FROM, TO– Line Event Table

Geog406-Network Analysis

Point Event Table

Point Event Table– Accident, signs– RouteID, Milieage

Geog406-Network Analysis

Line Event Table

Line Event table– Speed limit, Surface

material, traffic volume

– Route ID, FromM, ToM

Geog406-Network Analysis

Steps in Route Analysis

1. Create a route feature class2. Calibrate route data3. Display and query route events4. Edit route data

Geog406-Network Analysis

Create and Convert Route Data1. Create route feature class from

scratchOR

1. Convert an existing shapefile, coverage or feature class to route feature class

Geog406-Network Analysis

Create Route From Scratch

Route data can be stored in– Shapefiles– Coverages– Features

New routes can be added to the empty route feature class– Digitizing– Converting selected

features in a layer to routes and add the routes to the empty route data

Geog406-Network Analysis

Converting Existing Line Features to Route Data

– Features in the line layer should be assigned a route ID

Geog406-Network Analysis

Add Route Events

Geog406-Network Analysis

Calibrating Route Data

Improve accuracy of the distance measurement– Calibration points– Mileage reading

00

1510

20 28

10.5

022.5

16.530

Geog406-Network Analysis

Calibrating Route Data

Calibration points are stored in a point layerUse the Calibration WizardOR

Manual Calibration