Network analysis in gis , part 4 transportation networks

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TRANSPORTATION NETWORKS
 Transportation involves the movement of people and the shipment
of goods from one location to another.
 A geospatial model of a transportation network is comprised of
linear features and the points of intersection between them.
 A street network is a multilevel network that has a two-way flow
except for situations, such as one-way streets, divided highways, and
transition ramps.
 The modeling and analysis of networks has so many applications
that there is an entire branch of mathematics devoted to it known as
graph theory.
 In graph theory, linear segments of the network (e.g. road segments)
are referred to as edges and the points where the linear segments
connect are called nodes.

Transportation tasks include the following:
 Road type (width of road), pavement management, traffic
management and accident related data.
 As per the population within that area the transport network
structure should be redesigned.
 This may be to increase road width, make one ways, and identify
the parking area (multi floor parking).
 The use of GIS technology in development of Urbanization, the
transportation information system and management can provide a
very strong solution.
 Information related to transportation network is used in the efficient
planning, designing, construction, maintenance and
management of the transport system

Transportation tasks include the following:
 Calculating the quickest path between two locations
 Determining a trade area based on travel time
 Dispatching the closest ambulance to an accident
 Finding the best path and sequence to visit customers
 Routing a fleet of vehicles efficiently
 Determining the best location for a facility
 Finding the distance from every origin in a set of origins to every
destination in a set of destinations

Important Measures of Transport Networks
(i) The connectivity of networks;
(ii) The centrality within networks;
(iii) The spread and diameter of networks; and
(iv) Detours.
http://www.geographynotes.com/articles/4‐important‐measures‐of‐transport‐networks‐with‐
diagram/165

Connectivity and its Measurement
 The connectivity of a network may be defined as the degree of
completeness of the links between nodes.
 The greater the degree of connectivity within a transportation
network, the more efficient with that system.
 When a network is abstracted as a set of edges that are related to set
of vertices (nodes), a fundamental question is the degree to which all
pairs of vertices are interconnected.

 Beta Index (β): dividing the total number of arcs in a network by
the total number of nodes
Some characteristics
(i) β value for tree types of structures and disconnected networks would
always be less than 1. It would take zero values when there are no
edges in the network
(ii) β value for any network structure with one circuit would always be
equal to 1.
(iii) β value exceeds 1 for a complicated network structure having more
than one circuit.

Alpha Index (α):
 Non-planar graph as actual circuit / maximum circuits.
 The higher the index, the greater is the degree of connectivity
Gamma Index (ү): -ratio between the observed number of edges and
vertices
 The connectivity as measured by y index varies from a set of nodes
having no interconnection to the one in which every node has an
edge connected to every other node in the graph.

Centrality within a Network:
 Koning Number for describing the degree of centrality of any node
on a network
 The koning number for each node is calculated by adding up the
number of arcs from each other node using the shortest path
available.

Spread and Diameter of Networks
Pi Index (π):
 investigate the relationship between the total transportation network
as a whole and its diameter.
 The application of π index to transportation network would give a
numerical value which would be greater than or equal to one.
 Higher numerical values will be ascribed to more complicated
networks and it would reflect higher degree of development of the
network.

Spread and Diameter of Networks
Eta Index (n):
 useful when some spatial characteristic of the network are under
examination.
 This is also indicative of spread of a network.
 total network distance / number of arcs.
 This index is useful in examining the utility of a given transport
network.

Detours
 The straight routes between two places or direct routes (also known
as ‘desire line’) are the routes, which travellers used to follow
because of their shortest distance.
 But straight routes are, however, seldom to be found in reality; even
the most direct route in practice deviates from straight line. This
type of deflection is very common due to physical obstacles.
 Detour index= actual route distance/ straight line distance ×
100/1
 In other words, the detour index is the actual journey distance
calculated as a percentage of the desire line distance.
 It is obvious that lower the detour index, the more direct is a given
route. The detour index is used for assessing the effects which the
addition or abstraction of links produce in a given network.

Geographic Information Systems for Transportation (GIS-T)
 Refers to the principles and applications of applying geographic
information technologies to transportation problems.
 Access and analyze;
-spatially distributed nature of transportation related data
 Integration; the biggest advantage GIS
-bridge inventories; signage location, accident record and other
safety data; traffic volume and other operational data,
-Administrative, terrain, land use, demographic, environmental,
resource, and subsurface data.

Geographic Information Systems for Transportation (GIS-T)
GIS-T studies can be grouped into
 Data representations;
How can various components of transport systems be represented?
 Analysis and modeling;
How can transport methodologies be used in a GIS-T?
 Applications;
What types of applications are particularly suitable for GIS-T?

GIS-T; Potential applications in transportation planning
 Executive information system.
 Pavement management system.
 Bridge management.
 Maintenance management.
 Safety management.
 Transportation system management (TSM)
 Travel demand forecasting
 Corridor preservation and right-of-way
 Construction management
 Hazardous cargo routing
 Overweight/oversize vehicles permit routing.
 Accident analysis
 Environment impact
 Land side economic impact and value-capture analysis and Others.

Route
Closest Facility
Vehicle Routing
Problem
Location‐Allocation
Network Analysis
Services
Solve transportation problems Traffic
Service Area

Directions (Route) Service
 Point-to-point routing – Simple
Route
 Find the best route for visiting a
series of stops that minimizes
travel time or travel distance –
Optimized route
 Use live traffic conditions
 Driving directions in many languages

Finding the best route
 ArcGIS Network Analyst can find the best way to get from
one location to another or the best way to visit several
locations.
 The locations can be specified interactively by placing points
on the screen, by entering an address, or by using points in an
existing feature class or feature layer.
 The best route can be determined for the order of locations as
specified by the user.
 Alternatively, ArcGIS Network Analyst can determine the best
sequence to visit the locations.

What's the best route?
 Whether finding a simple route between two locations or one
that visits several locations, people usually try to take the best
route. But best route can mean different things in different
situations.
 The best route can be the quickest, shortest, or most scenic
route, depending on the impedance chosen. If the
impedance is time, then the best route is the quickest route.
 Hence, the best route can be defined as the route that has the
lowest impedance, where the impedance is chosen by the user.
Any valid network cost attribute can be used as the impedance
when determining the best route.

The quickest path is shown in blue and has a
total length of 4.6 miles, which takes 8
minutes
the length of the shortest path is 4.5
miles, which takes 9 minutes

Along with the best route, Network
Analyst provides directions with
turn-by-turn maps that can be
printed.

Traffic service
Visualize traffic speeds
Support for live, historical and
predictive traffic conditions
Traffic Incidents
Background layer to display results
from network analysis services
Data updated every five minutes

Closest Facility service
•Find the closest facilities from each incident
•Generate routes and driving directions
You can also…
Use live traffic conditions
Limit the search distance
Limit the number of facilities
to find
Travel from the facility to the incident

Finding the closest facility
 Finding the closest hospital to an accident, the closest police cars to
a crime scene, and the closest store to a customer's address are all
examples of closest facility problems.
 When finding closest facilities, you can specify how many to find
and whether the direction of travel is toward or away from them.
 Once you've found the closest facilities, you can display the best
route to or from them, return the travel cost for each route, and
display directions to each facility.
 Additionally, you can specify a cutoff cost beyond which ArcGIS
Network Analyst should not search for a facility.
 For instance, you can set up a closest facility problem to search for
hospitals within 15 minutes' drive time of the site of an accident.
 Any hospitals that take longer than 15 minutes to reach will not be
included in the results.

 The hospitals are referred to as facilities, and the accident is referred to as an incident.
 ArcGIS Network Analyst allows you to perform multiple closest facility analyses
simultaneously.
 This means you can have multiple incidents and find the closest facility or facilities to each
incident.

 The hospitals are
referred to as facilities,
and the accident is
referred to as an
incident.
 Network Analyst allows
you to perform multiple
closest facility analyses
simultaneously.
 This means you can have
multiple incidents and
find the closest facility
or facilities to each
incident

Finding service areas
 With Network Analyst, you can find service areas around any
location on a network.
 A network service area is a region that encompasses all
accessible streets, that is, streets that lie within a specified
impedance.
 For instance, the 5 or 10 -minute service area for a point
includes all the streets that can be reached within five or ten
minutes from that point.

What is accessibility?
 Accessibility refers to how easy it is to go to a site.
 In ArcGIS Network Analyst, accessibility can be measured in
terms of travel time, distance, or any other impedance on the
network.
 Evaluating accessibility helps answer basic questions, such as,
"How many people live within a 10-minute drive from a movie
theater?" or "How many customers live within a half-kilometer
walking distance from a convenience store?"
 Examining accessibility can help you determine how suitable a
site is for a new business.
 It can also help you identify what is near an existing business to
help you make other marketing decisions.

Evaluating accessibility
 One simple way to evaluate accessibility is by a buffer distance
around a point.
 For example, find out how many customers live within a 5-
kilometer radius of a site using a simple circle.
 However, considering people travel by road, this method won't
reflect the actual accessibility to the site.
 Service networks computed by ArcGIS Network Analyst can
overcome this limitation by identifying the accessible streets
within five kilometers of a site via the road network.
 Once created, you can use service networks to see what is
alongside the accessible streets, for example, find competing
businesses within a 5-minute drive.

 Multiple concentric service areas show how accessibility changes with an increase in impedance.
 It can be used, for example, to show how many hospitals are within 5-, 10-, and 15-minute drive times
of schools.

 Multiple concentric service areas show how accessibility changes with an increase in
impedance.
 It can be used, for example, to show how many hospitals are within 5-, 10-, and 15-
minute drive times of schools.

Creating an O-D cost matrix
 With ArcGIS Network Analyst, you can create an origin–
destination (OD) cost matrix from multiple origins to
destinations.
 An OD cost matrix is a table that contains the total impedance
from each origin to each destination.
 Additionally, it ranks the destinations that each origin connects to
in ascending order of the time it takes to travel from that origin to
each destination.
 The paths from each origin to each destination are represented as
straight lines on the map, which can be symbolized by color,
representing which point they originate from; or by thickness,
representing the travel time of each path.

The straight lines can be symbolized in various ways, such as by color,
representing which point they originate from, or by thickness, representing the
travel time of each path.

Service Areas (Drive Times) service
You can also…
- Solve for many locations
- Use multiple drive time values
- Analyze for different times of
the day
- Specify the direction of travel
Find the area you can reach from a location in a given time period

Location‐Allocation service
Determine the best location for a facility, based on demand conditions
• Choose from many
different analysis types
• Limit the capacity of
facilities
• Analyze for different
times of day

Out of the current set of fire stations, nine fire stations can close, and a minimum of seven are
needed for the department to still be able to respond to emergencies within three minutes.

Vehicle Routing Problem (Fleet Routing) service
Route a fleet of vehicles to service a set of orders
You can also specify…
Vehicle capacities
Driver specialties
Work breaks
Time windows on orders

Vehicle Routing Problem (Fleet Routing) service

1. http://webhelp.esri.com/arcgisdesktop/9.2/index.cfm?TopicName=Types_of_ne
twork_analyses
2. https://www.e‐education.psu.edu/geog497c/
References

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