Network Analysis

Network Analysis

Aman Arora

Geographical AnalystLepton Software

Mail Id: [email protected]

[email protected]

MARCH, 25, 2011

Aman AroraGeographical Analyst

Lepton Software

Mail Id: [email protected]

[email protected]

Introduction

• Network: A system of interconnected elements, which represent possible routes from one location to another.

• Analysis: A systematic examination of something in detail in order to understand it better or draw conclusions from it.

• Network Analysis: Any method of solving network problems such as traversability, rate of flow, or capacity, using network connectivity called Network Analysis.

• It is used for identifying the most efficient routes or paths for allocation of services. This involves finding the shortest or least-cost manner in which to visit a location or a set of locations in a network.

Which Software allows you to create Network Dataset and do Network Analysis?

• ArcGIS • MapInfo• Bison Atlas• TA Mapper etc.

ArcGIS Network Analysis

• ArcGIS Network Analyst allows you to solve common network problems, such as finding the best route across a city, finding the closest emergency vehicle or facility, identifying a service area around a location, servicing a set of orders with a fleet of vehicles, or choosing the best facilities to open or close.

• ArcGIS Network analyst follows Dijkstra’s Algorithm to solve route problem.

• ArcGIS Network Analyst work on Network Datasets.

Network Dataset• Network datasets are well suited to model transportation

networks. They are created from source features, which can include simple features (lines and points) and turns, and store the connectivity of the source features.

Structure of Network Dataset

• Network data structures are methods for storing network data sets in a computer in order to support a range of network analysis procedures.

• Network data sets are among the most common in GISci and include transportation networks (e.g., road or railroads), utility networks (e.g., electricity, water, and cable networks), and commodity networks (e.g., oil and gas pipelines), among many others.

• Network data structures must store the edge and vertex features that populate these network data sets, the attributes of those features, and, most important, the topological relationships among the features.

• All analytical parts in Network Analyst is carry out on the Network Dataset, so it is very important to make this dataset topologically perfect.

Types of NA (In ArcGIS)

• New Route• New Service Area• New Closest Facility• New OD Cost Matrix• New Vehicle Routing Problem (VRP)• New Location-Allocation

New Route• 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.

Time Impendence

• In this example below, the first case uses time as an impedance. The quickest path is shown in blue and has a total length of 4.5 miles, which takes 8 minutes to traverse.

Distance Impedance

• While In this case, distance is chosen as the impedance. Consequently, the length of the shortest path is 4.4 miles, which takes 9 minutes to traverse.

New Service Area

• 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 example, the 10-minute service area for a facility includes all the streets that can be reached within 10 minutes from that facility.

Accessibility (Through Polygons)

Accessibility and Accessible Roads (Through Polylines)

How many hospitals are within 5-, 10-, and 15-minute drive times of schools

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.

• For example, you can set up a closest facility problem to search for hospitals within 15 minutes' drive time of the site of an accident.

Closest facility for hospitals within 15 minutes' drive time of the site of an accident

OD cost matrix

• An OD cost matrix is a table that contains the network impedance from each origin to each destination.

• It ranks the destinations that each origin connects to in ascending order based on the minimum network impedance required to travel from that origin to each destination.

• The best network path is discovered for each origin-destination pair, and

• The cost is stored in the attribute table of the output lines.

• Even though the lines are straight for performance reasons, they always store the network cost, not straight-line distance.

OD Cost Matrix Analysis

OD Cost Matrix Analysis

Vehicle Routing Problem (VRP)

• VRP is a decision making module of Network Analyst, which determine, manage, plan, analyze and finalize the most efficient route for a fleet of vehicles.

• The objectives in solving such vehicle routing problems (VRP) are to provide a high level of customer service by honoring any time windows while keeping the overall operating and investment costs for each route as low as possible.

• ArcGIS Network Analyst provides a vehicle routing problem solver that can be used to determine solutions for such complex fleet management tasks.

Vehicle Routing Problem (VRP)

Location-Allocation

• Location-allocation helps you choose which facilities from a set of facilities to operate based on their potential interaction with demand points. It can help you answer questions like the following:

Given a set of existing fire stations, which site for a new fire station would provide the best response times for the community?

If a retail company has to downsize, which stores should it close to maintain the most overall demand?

Where should a factory be built to minimize the distance to distribution centers?

• In these examples, facilities would represent the fire stations, retail stores, and factories; demand points would represent buildings, customers, and distribution centers.

• The objective may be to minimize the overall distance between demand points and facilities.

• Maximize the number of demand points covered within a certain distance of facilities.

For instant example map below shows the results of a location-allocation analysis meant to determine which fire stations are redundant. The following information was provided to the solver: an array of fire stations (facilities), street midpoints (demand points), and a maximum allowable response time. The response time is the time it takes firefighters to reach a given location. The location-allocation solver determined that the fire department can close several fire stations and still maintain a three minute response time.

Location-Allocation

Location-Allocation

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

References:

Web Resources:• www.wikipedia.com• www.esri.com/forum/extension/networkanaysis.com• www.youtube.com

Other Resources (Books, eBooks etc.)• ArcGIS Desktop Help• Encyclopedia of Geographic Information System.

THANK You