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Overview of Network Analyst

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1 Overview of Network Analyst

2 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. What is a network?  Any set of connected linear features can be considered a network. You probably use networks everyday, although you usually aren't aware of it. For example, when you want to find the fastest way to get to work, school, or the shopping mall, you look at a map to determine a route or get directions from a friend. In both cases, you're plotting a path through a street network. A network doesn't have to be streets or roads, although they are probably the networks you are most familiar with. Networks can represent rivers, pipelines, and utilities. The route doesn't actually have to exist in the real world as a set of linear features. An airline route or a course charted for a ship can also be represented as a network. Because a network is a set of interconnected lines, you can model the movement of goods, services, energy, information, or even people throughout the network.

3 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.

4 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.

5 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.

6 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.

7 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.

8 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. Modeling the flow of goods and services  Network Analyst lets you simulate real-world conditions by modeling the flow or movement of resources through a network. You can access different attributes in the database or enter information interactively to alter the conditions of a problem. Whether the conditions change day to day or even minute by minute, with Network Analyst, you can alter the conditions and run the model again and again to get a different solution to your problem. For example, you can obtain very different solutions to a problem by applying different units of measure, such as time or distance, to a single set of spatial data. In the example here, the shortest path is based on the length of the streets and the fastest path is based on the time it takes to traverse each street during a typical workday morning. Network Analyst gives you two different solutions because you are actually asking two different questions.

9 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.).

10 Path finding with real-time info
Adding real-time data, such as accident information, can lead to paths that change minute by minute. Another way to increase the accuracy of the results you get from Network Analyst is to integrate real-time information into the solution. In the example below, the fastest path is based on the time it takes to traverse each street. One of the intersections along the route, however, has been blocked off due to an accident. While the travel information, based on minutes, is read directly from the network theme's attribute table, the accident information is entered interactively or read from a file, in real time, using current police traffic reports. Because this example uses real-time information, the solution you get now could be very different from the solution you get an hour later.

11 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 Modeling accessibility  Accessibility is a measure, usually in units of distance or time, of how easy it is to get to a location or locations. For example, 12,350 people may be able to drive to the hospital emergency room within 12 minutes; 2,125 potential customers may live within a 1.5 kilometer (walking) distance of a shopping center; and a fire truck can reach 3,000 homes and businesses within 7.5 minutes. The simplest way to model accessibility is to use a straight-line distance or radius that extends outward from a specific location. While this may be useful if you're in an airplane or a boat, it doesn't reflect the way people move from one location to another on land. The same network that you use to model the flow of resources can be used to model accessibility. All you need to do is add the location (the site) you're going to or the location you're coming from. Newtork Analyst creates two themes that display a site's accessibility. The polygonal area that contains the set of lines that meet your criteria is called a service area theme, and the lines it contains are called the service network theme.

12 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).

13 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.

14 Service line network Snet1 contains the lines (streets) or portions of lines that can get to the hospital within 12 minutes.

15 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

16 Examples Three examples that demonstrate the basic functionality of Network Analyst (from top). 1. Finding the best route 2. Finding the closest facility 3. Determining service areas

17 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. Find the optimal path Using Network Analyst, you can find the path that will reach specified locations in the most efficient order. The path can be the shortest path or the fastest path. Network Analyst also gives you the option to return to the point of origin when defining a path.

18 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 Network Analyst provides you with directions for navigating a route. The directions can be customized to include different units, such as time or distance, or landmarks to help you find your way while navigating the route.

19 Finding the closest facility
This example shows the closest emergency room to a traffic accident. Find the closest facility Using Network Analyst, you can find the closest facility to a location as well as the path to and from the facility.

20 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. You can find the distance and directions to all the facilities.

21 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. Map accessibility You can also find which locations or areas are accessible to a specific site. Network Analyst shows you which lines, or portions of lines, can be accessed within a specific time limit or distance; or the area that can reached using the same criteria. You can use this information to find which clients the site can service.

22 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.

23 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. Define service areas Service areas can be defined as generalized polygons that can include portions of the study area that are not directly accessible by the streets in the service network. Or, the service area can be defined to include only the areas that can be reached by the service network.

24 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 Service areas can be nested or even overlap. Using this information you can determine the quality of service to your clients or if some clients are being serviced by more than one site.

25 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. By integrating different Network Analyst tools you can solve many real-world problems. In the example below, Network Analyst is used to find accessible bus stops and the bus routes they service.

26 Finding routes Best 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. Finding routes  A path between two locations is called a route. "Finding the best route" can be interpreted in different ways. For example, does the best route mean the shortest path between two locations or the fastest path between them? Do you want the fastest route at 9:00 AM or the fastest route at 4:00 PM? The attribute used to define a route is called the cost attribute, or just cost, and can represent any unit. Any numeric attribute in the theme's attribute table or in a table related to the theme attribute table can be used as the cost.

27 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.

28 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. A route can visit several locations, called stops, between its origin and destination. In addition to finding the shortest or fastest route between stops, Network Analyst can also find the most efficient order in which to visit them. For example, you could find the most efficient package delivery route for an express mail service. The route would visit all the stops in the shortest possible time. Along with a visual display of the route, Newtork Analyst provides a set of useful directions that tell you how to navigate it.

29 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. Finding closest facilities  A facility is anything or any place that provides services or products. Examples of facilities might be a fire station, a warehouse, or a service station. When you find the closest facility, you find the closest facility to a specific location, known as an event. Finding the closest facility is similar to finding the best route. Network Analyst computes the best route (i.e., shortest or fastest path) to each facility, then chooses the facility with the best route. For example, suppose you want to find the nearest service station that has a tow truck (the facility) to the location of a stranded motorist (the event). In most cases, you also want to know how to get to the service station, or, if you're the tow truck driver, how to get to the stranded motorist. Network Analyst provides you with a graphic display of the route as well as directions for navigating the route.

30 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.

31 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 …… 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. An example of a service area might be the area around a pizza parlor that can be reached within a specific time. Because Network Analyst represents each service area as a polygon, you can use ArcView's spatial analysis tools to find which customers and how many customers are in a service area. You can even determine which service areas overlap and find the customers that are serviced by more than one pizza parlor. One-way streets, construction work, or even the time of day can increase the travel time to or from a facility. You can specify whether the direction of travel is from the surrounding region to the site (e.g., customers traveling to the pizza parlor) or from the site to the surrounding region (e.g., the pizza delivery vehicle traveling to homes or businesses). Accounting for these conditions allows you to model real-world conditions more accurately.

32 Example: Routing supply trucks
Route trucks around blocked streets and highways. Blocked streets are displayed in yellow. Example Routing supply trucks  After an earthquake, truckloads of emergency medical supplies are arriving from all over the country. Ron and his coworkers must route the supply trucks around blocked streets and highways to functioning hospitals and clinics. Ron uses Network Analyst to find the fastest routes and create directions for the truck drivers. The first thing Ron does is highlight the damaged and closed streets in the view.

33 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. Ron wants to find a route through the City Streets theme that most efficiently reaches each point in the Hospitals & Clinics theme. First, he needs to define the problem for Network Analyst. He chooses Find Best Route from the Network menu. The Route1 problem definition dialog displays. This is where Ron defines the stops (hospitals and clinics) along the route.

34 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. Ron can define the stops in three ways. He can click on locations in the view with the Add Location tool . He can also type in street addresses by clicking the Add Location by Address button . Or, as he does now, he can click the Load Stops button in the problem definition dialog to load the stops from the Hospitals & Clinics point theme.

35 Displaying stops Network Analyst places a green square, indicating a route stop, at the location of each hospital or clinic. Now each hospital and clinic is listed as a stop along the route in the Label column. The names are taken from the Label attribute in the Hospitals & Clinics attribute table. In the view, each point in the Hospitals & Clinics theme has a green square over it, indicating that it's a potential stopping point. (Notice that one potential stop is in the highlighted zone of closed streets and is therefore unreachable by truck.) There's also a new, empty theme, called Route1, in the view. This is where Network Analyst will display the best route.

36 Find paths of the lowest costs
Distance Travel time Other attributes Not distance Network Analyst determines the best route by finding the route with the lowest "cost." Cost can be defined as distance, travel time, or some other attribute. By default, a route's cost is found by adding the lengths of all the line segments in the route. Network Analyst performs this calculation for all possible routes that pass each stop and chooses the route with the least cost. This is the shortest route. Under normal circumstances, finding the shortest route is fine, but with the traffic congestion caused by closed freeways and streets, the shortest route may take longer to drive. The best route in this case is not the shortest, but the fastest. Ron changes the cost field to Drivetime. Network Analyst will find the route with the lowest cost in terms of time rather than distance. The Route1 problem definition dialog reflects this change. The cost column is labeled "minutes" instead of "miles." 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.

37 Solutions The Solve button
The travel time between stops is shown as well as which stops cannot be reached. Ron has provided all the necessary information, so he clicks the Solve button . Network Analyst finds the fastest route to each hospital and clinic. It displays the time that it takes to drive the entire route in the Total Route Cost field at the top of the dialog. The minutes column shows the elapsed time from the route's starting point to each hospital or clinic. Network Analyst tells him that Desert Clinic (the one located in the section of closed streets) couldn't be reached. This clinic will need its supplies delivered by helicopter.

38 Displaying solution routes
The completed route is displayed in the view and directions for navigating the route are generated. The route also displays in the view. Notice that it avoids the damaged streets. This route may not be the shortest in terms of distance, but it has the shortest drive time. Ron can label the street names and print a copy of the map for each supply truck driver. Because many drivers are unfamiliar with the area, he'll also use Network Analyst to print a set of directions.

39 Example: Finding the closest facility
Street network and associated themes (important landmarks, hospitals and clinics, and fire stations). New, empty Theme to Store solutions Choose Find Closest Facility Example Finding the closest facility   Ron now has an additional problem following the earthquake. The Fire Department has been called to a major blaze in the northeast part of town, but the nearest fire station is damaged and not operational. Because of road closures, the next closest station may or may not be able to get a fire engine to the scene. Ron has the most up-to-date road closure information stored in ArcView, so he will use Network Analyst to determine which station should respond. He also needs a set of directions to guide the engines along passable roads. To solve this network problem, Ron chooses Find Closest Facility from the Network menu. An empty theme called Fac1 (Facilities theme 1) is created in the view. This theme will contain Network Analyst's solution to the problem Ron defines. After earthquake, find gas stations that still function

40 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. In the Fac1 problem definition dialog, Ron sets Facilities to the Fire Stations theme and tells Network Analyst to find one facility. He chooses the Travel to Event option because the fire engines will travel from the station to the fire. Because time is of the essence, Ron clicks the Properties button and chooses minutes as the route cost instead of miles. Next, he enters the location of the fire in the Event field. Since there's only one event to locate, Ron clicks the Add Location by Address button . When the Locate Address dialog appears, he types in the fire's location.

41 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. In the Fac1 problem definition dialog, the Event box now shows the fire's location. Ron has finished defining the network problem, so he clicks the Solve button . Network Analyst calculates which station in the Fire Stations theme will be able to respond most quickly and displays the name of the closest station in the Label field. The estimated travel time is shown in the minutes field. The Solve button

42 The solution view The route from Sta 3 West to the fire is displayed in green in the view. The view shows the fastest route to the fire from the selected station. It's not the closest station, but it's the one that can respond most quickly under the present conditions. Just as he did for the hospital route, Ron creates directions and customizes them to show landmarks, full street names, and distances in miles instead of minutes. The engines are on their way with directions that guide them around the traffic congestion to the fire.

43 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 Example Finding service areas  Ron and his coworkers have been asked to identify those areas where ambulances can't reach people within 10 minutes. Temporary tent clinics will be set up in these areas and helicopters will be used to transport seriously injured people to hospitals. Ron will use Network Analyst to determine the areas that are reachable over open roads within 10 minutes of each hospital and clinic. He'll also produce a map showing the less accessible areas that need medical services. To solve this network problem, Ron chooses Find Service Area from the Network menu. Two empty themes are created in the view, Snet1 and Sarea1. These themes will contain the solution to the service area network problem. Snet1, a line theme, will show all city streets within 10 minutes of a hospital or clinic. Sarea1, a polygon theme, will show polygons that cover the 10-minute drive time area around each hospital. There will be one polygon for each hospital or clinic and it will encompass the area that's reachable within 10 minutes.

44 Definition dialog Sarea1 and Snet1 definition dialog
The Sarea1 and Snet1 problem definition dialog also displays. Ron loads the Hospitals & Clinics theme by clicking the Load Sites button. He sets the properties to display minutes instead of miles, then types "10" in the minutes field for each hospital or clinic. This is the maximum drive time an ambulance can take to reach an injured person.

45 (blocked streets are not part of the areas)
Solutions Compact area check box Draws service areas precisely Leaves it unchecked for smooth areas (blocked streets are not part of the areas) Ron also checks the Compact area check box. If this box isn't checked, Network Analyst will create smooth polygon shapes for the service area to make the map look better for presentation. If Compact area is checked, Network Analyst draws the 10-minute service area precisely, even though the polygon outline will be jagged. Ron doesn't care how the map looks; he wants the outlines of the 10-minute service area to be exact. After Ron clicks the Solve button , Network Analyst creates lines in the Snet1 theme showing all the streets within a 10-minute drive of medical help. Network Analyst also creates polygons in the Sarea1 theme showing the 10-minute drive time zone around each hospital and clinic. Areas not included in these zones will need temporary clinics and helicopter service. Ron can print these maps and give them to the planners in charge of getting medical service to the entire city. As repair crews reopen streets, Ron can easily update the maps and directions he's created. He can change the street conditions in the attribute table, redisplay the problem definition dialog, and create a new solution.

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

47 Summary  In this lesson, you learned what a network consists of and the basic concepts of modeling resource flow and accessibility. Network Analyst can be used to solve a variety of network problems and these problems can be quite complex. You model network problems using a cost field contained in the network theme's attribute table and point features called stops, events, or facilities. Real-time information can be added to the model to better portray real-world conditions. This lesson introduced you to Network Analyst's functionality, including how to create a simple route, find the nearest facility, and define a simple service area.

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