Lecture 3 - California State University, NorthridgeLecture 3 Network Analysis Geog406-Network...
Transcript of Lecture 3 - California State University, NorthridgeLecture 3 Network Analysis Geog406-Network...
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