Overview of Network Analyst

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What is a network?

• Any set of connected linear features can be consider a network.

• Can be real objects– Streets, rivers,

• Can be symbolic objects– Airline routes, navigation routes

• Can be ideas– Social networks, etc.

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Network example 1

• This network theme represents city streets and highways. Several theme attributes, such as speed limits, the number of lanes a street has, or which streets are one-way or two-way, can affect the flow of goods and services through a network.

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Network example 2

• Utilities can also be network themes. In this example, the diameter of the waterlines, the system's water pressure, and the location of control valves can affect the flow of the water through the network.

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Network example 3

• River systems can be represented as a network or a series of networks. Some systems may not connect while other systems may connect naturally or may be connected by canals. The location of locks, river width, river depth, and current can affect the analysis.

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Network example 4

• Knowing the conditions of specific pipelines and which pipelines are connected can help gas suppliers move gas more efficiently to different regions of North America.

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Network example 5

• Even though airline routes do not exist as linear features on the surface of the Earth, their flight paths and the locations of connecting airports can still be represented as a network.

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Shortest path

• This path represents the shortest linear distance between the two locations. By default, a network theme's coordinate system units are used to calculate linear distance.

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Fastest path

• This path represents the fastest path between the same two locations used in the previous example. Fastest paths are based on time and you can use any measure of time you choose (seconds, minutes, hours, etc.).

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Path finding with real-time info

• Adding real-time data, such as accident information, can lead to paths that change minute by minute.

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Accessibility

• Accessibility– Measured in distance or in time– Measures how easy it is to get to a

location or locations

– Two themes for a site’s accessibility• Polygonal area

– The set of lines that meet pre-defined criteria– Called service area theme

• Lines– Service network theme

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Service area/network

• When you create a service area, Network Analyst creates both a service area polygon (Sarea1) and a service network of lines (Snet1).

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Service area

• In this example, Sarea1 is a polygon theme that represents the area of the city that can get to the hospital within a 12-minute drive time.

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Service line network

• Snet1 contains the lines (streets) or portions of lines that can get to the hospital within 12 minutes.

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Network Analyst

Network Analyst lets you: • solve different routing problems • display customized directions • find the closest facility • find the distances to all facilities • find locations that are accessible to a facility

using service areas and networks • create multiple nested or overlapping

service areas

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Examples• Three examples that

demonstrate the basic functionality of Network Analyst (from top).1. Finding the best route2. Finding the closest facility3. Determining service areas

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Finding the optimal path

• This path represents a delivery truck route.With Network Analyst, the dispatcher can define a route that will stop at each restaurant in the most efficient order and return to the warehouse.

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Directions

• By default, directions generated by Network Analyst include street names and the distance units of the theme. You can customize the directions to include things like landmarks

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Finding the closest facility

• This example shows the closest emergency room to a traffic accident.

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Distance and directions• This example shows the

paths and the distances to all the facilities. This information could be very useful to the ambulance dispatcher if the closest facility was unavailable.

• Network Analyst gives you the distances to each facility or, if you want to find the closest facility using time, the time it takes to get to each facility.

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Map accessibility – within a distance

• This example shows the streets, or portions of streets, that are within a specified distance of a shopping mall. You can also see that some of the ATMs, banks, and restaurants are located on these streets.

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Service area polygon – within 2 km

• A service area polygon created by Network Analyst can be used with ArcView's spatial analysis tools to find locations within 2 kilometers of the mall. Once identified, you can find the closest facility to the mall.

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Define service areas

• This example shows that parts of the city contained in the service area are not actually reached by the streets in the service network.

• A service area was created using only the areas of the city that can actually be reached by the service network.

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Nested service areas

• This example shows which areas are located within specified distances of pizza restaurants. Some portions of the city are serviced by more than one restaurant

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Accessible bus stops and bus routes

• This example shows areas within a 10-minute walking distance of different bus stops (service area and network) and which bus routes (find best route) are serviced by the stops.

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Finding routesBest routes?

– Depending on attributes used

• This route was created using an attribute that contains travel times for 9:00 AM. Factors such as one-way or two-way streets, traffic load, the number of lanes, speed limits, and even the percent of grade can affect the travel time.

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Another best route?

• The same starting and ending locations are used, but this best route was created using the attribute for travel times at 4:00 PM.

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Stops and path visiting them• Top: Routes can include

stops that must be visited. You can specify the order of the stops or let Network Analyst find the most efficient order for you.

• Bottom: Directions tell you how to navigate the route and can include key landmarks or user-defined travel units.

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Finding closest facilities

• A Facility is anything or any place that provides services or products.

• Calculate best routes to all facilities.• Then choose the facility that has the

best route.

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Finding paths to facilities• Top: Network Analyst

calculates the best path to all facilities and then chooses the best path from all the best paths. In this example, the location of the motorist was entered interactively as an address and the service station addresses were read from a file.

• Bottom: These directions tell the tow truck driver how to find the motorist. Traveling from the facility to the event or traveling from the event to the facility will result in different directions and possibly different routes.

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Defining service areas

• A service area measures a site’s accessibility by defining a region that includes all the lines within the network that are accessible to the site.

• Overlapping and nested service areas are individual polygons.

Travel cost: by time by distance by time of day ……

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Example: Routing supply trucks

• Route trucks around blocked streets and highways.

• Blocked streets are displayed in yellow.

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Example: Routing supply trucks

• First define stops• Then choose routing

method

• The Route1 problem definition dialog. Each dialog is named according to the route theme it will create.

After earthquake,Some streets were blocked.Need to find ways to hospitals.

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Defining stops• Add Location tool• Add Location by Address tool

Top: Load Stops dialog showing Hospitals & Clinics point theme as the selected stops theme.

Bottom: Route1 problem definition dialog with the names of the Hospitals & Clinics.

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Displaying stops

• Network Analyst places a green square, indicating a route stop, at the location of each hospital or clinic.

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Find paths of the lowest costs• Costs

– Distance– Travel time– Other attributes

Properties dialog showing DRIVETIME as the Cost field and minutes as the Working units. Network Analyst converts from minutes, seconds, or hours on the fly and displays the units in the directions.

Not distance

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Solutions• The Solve button

• The travel time between stops is shown as well as which stops cannot be reached.

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Displaying solution routes

• The completed route is displayed in the view and directions for navigating the route are generated.

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Example: Finding the closest facility

• Street network and associated themes (important landmarks, hospitals and clinics, and fire stations).

After earthquake, find gas stations that still function

New, emptyTheme to Store solutions

ChooseFind Closest Facility

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Example: find facility• Top: The facility that

Network Analyst will find is a point feature in the Fire Stations theme.

• Bottom: The Locate Address dialog. If you have created an address index for the network theme, you can use an address to create a stop, facility, or site.

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Solution

• After the network problem is solved, you can see which fire station can respond most quickly to the event and the time it will take to drive from the fire station to the event.

The Solve button

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The solution view

• The route from Sta 3 West to the fire is displayed in green in the view.

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Example: finding service area

• To identify areas that ambulances cannot get to in 10 minutes.

• Use Find Service Area function• Two empty themes are created (Snet1 and

Sarea1) for storing solutions

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Definition dialog

• Sarea1 and Snet1 definition dialog

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Solutions

• Compact area check box– Draws service areas precisely– Leaves it unchecked for smooth areas

(blocked streets are not part of the areas)

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Exercises

• Ex12 – Create a simple route• Ex13 – Find the closest facility• Ex14 – Find service areas

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