The ArcView Network Analyst extension module allows the user to solve 3 categories of network analysis problems; Find Best Route, Find Closest Facility and Find Service Area. If you need to conduct more complex analyses than these 3 default options available, you can do this using Avenue scripts.

Find Best [...]]]> ARCVIEW NETWORK ANALYST

The ArcView Network Analyst extension module allows the user to solve 3 categories of network analysis problems; Find Best Route, Find Closest Facility and Find Service Area. If you need to conduct more complex analyses than these 3 default options available, you can do this using Avenue scripts.

Find Best Route problems involve finding the “least cost impedance” path on the network between two or more stops. Find Closest Facility pertains to finding the distances from an event to the nearest facilities, or vice versa, finding the distance from a facility to one or more events. Find Service Area determines the area that a particular facility can serve within a given time or cost frame.

This tutorial comes complete with exercise data and solutions. You can to find the download link for the data and the solution to the exercises in the menu bar.

Make the View window active,View > Add Theme > Select slcroads.shp Repeat this for the following themes: facilities.shp, events.shp, stops.shp

The first time you perform a network analysis on a line theme, Arcview Network Analyst [...]]]> To perform a network analysis using Arcview Network Analyst, a road theme must be present in your View window:

Make the View window active,
View > Add Theme > Select slcroads.shp
Repeat this for the following themes: facilities.shp, events.shp, stops.shp

The first time you perform a network analysis on a line theme, Arcview Network Analyst will build the topology, create a cost matrix and then run the analysis. In a large network, this may take some time. The next time you run an analysis on the same network, the topology is then already present, and the analysis runs much quicker. However, as soon as you edit the theme attribute table, Arcview Network Analyst will have to rebuild the topology again before running any analysis.

FIND BEST ROUTE With the slcroads.shp theme active, Network > Find Best Route

Arcview Network Analyst now adds a route theme to your view and presents you with a new dialog box.

You now have two options to add the stops for which you want to calculate a route, either [...]]]> Download data first!

FIND BEST ROUTE
With the slcroads.shp theme active,
Network > Find Best Route

Arcview Network Analyst now adds a route theme to your view and presents you with a new dialog box.

You now have two options to add the stops for which you want to calculate a route, either by interactively selecting stops graphically from the view, or by loading a point theme that holds the stops. First, let’s try to select them graphically.

SELECTING STOPS INTERACTIVELY
Click the Add Location icon in the menu bar:

Then click in the view to select stops.

These are added to the dialog box as you click them.

You can change the order of stops by highlighting (clicking) them, and then use the arrow buttons; you can also delete stops by clicking the delete “X” button. In addition you can use the check boxes to choose whether you want Arcview Network Analyst to find the best order of stops, and/or whether you want to return to the origin (the first stop in the list). Properties allows you to choose the shortest path based on shortest distance (default) or least cost (minutes or other cost units).

Just add a couple of stops, then click the Solve icon:

Arcview Network Analyst will now build the topology and run the analysis. Be patient! When done, Arcview Network Analyst will add a display the route in your window.

Click Directions.

This gives you turn-by-turn directions for the entire route.

Click Done.

With the dialog box still open, check the Find best order box, then click the Solve icon again.
Did the route change?

With the dialog box still open, click Properties, select Minutes as your Cost field, click OK, click the Find Solve icon. Did the route change?

If you want to save the different alternatives as different routes, you need to save them separately:

Make the calculated route active in the View window.
Theme > Convert to Shapefile > Select a name and a folder > Accept to add the theme to the view.

When done running and saving the different alternatives you want to display, delete the default route theme:

Make the default route theme active,
Edit > Delete Theme

SELECTING STOPS FROM A STOPS THEME
Make the road theme active,
Network > Find Best Route > Load Stops > Select stops.shp .
Try the same variations as before.

SETTING RESTRICTIONS
If you select one (or more) arc(s) prior to Solve, this prohibits travel on this arc. Try it out! This is an easy way to model restrictions without editing the attribute table.

Make the road theme active, Network > Find Service Area

Arcview Network Analyst now adds a service area and service network theme to your view and a similar dialog box as for

Find Best Route appears.

As before, you can select one or more centers interactively. Choose the cost units; [...]]]> SELECTING CENTERS INTERACTIVELY

Make the road theme active,
Network > Find Service Area

Arcview Network Analyst now adds a service area and service network theme to your view and a similar dialog box as for

Find Best Route appears.

As before, you can select one or more centers interactively. Choose the cost units; use the default distance, or use Properties to set your units. Then enter the cutoff value for the service area. You can do a stepwise analysis to see what areas are covered within a certain distance/cost. If the network has differing to-from directions and costs, select the direction of travel.

SELECTING CENTERS FROM A THEME
Make the road theme active,
Network > Find Service Area

Select Load Sites > Select sites.shp
Run analysis as above.

Make the road theme active, Network > Find Closest Facility

Arcview Network Analyst now adds a facility theme to your view and a similar dialog box as for Find Best Route appears.

Select facilities.shp from the Facilities drop-down list.

The number of facilities to find is the number of [...]]]> SELECTING FACILITIES INTERACTIVELY

Make the road theme active,
Network > Find Closest Facility

Arcview Network Analyst now adds a facility theme to your view and a similar dialog box as for Find Best Route appears.

Select facilities.shp from the Facilities drop-down list.

The number of facilities to find is the number of nearest facilities to the event that you wish to find. If you for example are looking for the nearest ATM to your current location and your facilities list contains 200 ATMs, you would probably only the nearest 5 or so.

The cutoff-cost is the distance/cost where you want the search to stop. This is as far as you want to travel in search for the facility. Select the Properties button if you want to change the cutoff-cost from the default distance units to your specific cost units, for example minutes. Leave this line empty or enter a value.

If you have a directional network, where the cost of travel differs depending on which direction you are traveling in along the arc, select Traveling to/from event as appropriate. For example, if the facilities are hospitals, and the events are accidents, you can then analyze whether it is faster to travel to a given hospital from the accident, or whether it is faster to travel from a different hospital to the accident scene. This may be the case if there are restricted turns and roads depending on which direction you are traveling in. If the cost of traveling is independent of the direction, either choice is valid.

Click the Add Location icon to add an event and click the view to place your event where you want it to be.
Click the Solve icon.

After solving, the dialog box now displays the distance/cost to the number of facilities that are within the search radius. Select a particular facility to see it highlighted in the view.

SELECTING EVENTS FROM AN EVENT THEME
In the dialog box above, select Load Events, select the events file events.shp that you have already loaded into your view, then select the desired event from the drop-down list. Click the Solve icon.

Tip: If you would like to know the distance from one or more facilities to all individual events, simply reverse the input: Enter events instead of the facilities, and enter facilities where the events should be.

Unfortunately, you cannot expect the network to be fully prepared for you every time you do a network analysis. There’s a lot of work behind the scenes before you can actually perform a network analysis. This includes setting the travel cost for each arc, defining directions and one-way [...]]]> SETTING UP A ROAD NETWORK

Unfortunately, you cannot expect the network to be fully prepared for you every time you do a network analysis. There’s a lot of work behind the scenes before you can actually perform a network analysis. This includes setting the travel cost for each arc, defining directions and one-way streets, managing restricted turns and most important, address matching.

First, add the nonetwork road theme to your view. The roads look the same as before, but they lack much of the necessary network information.

You can still perform a network analysis with just this line theme present. However, the default cost then is equal to distance traveled. There are no directional restrictions (you may go the wrong way down a one way street, or use the wrong side on the freeway, and turn wherever you want). Routing by address is also more difficult, albeit possible, since you can always select your stops graphically at the approximate position, if you have enough local knowledge to know where you are in the view.

Travel cost is the average cost of traveling along a link. By default this is distance, i.e. the length of the link. However, you can define your own cost units, using for example the average time in minutes that it takes to traverse the link based on average speed along the [...]]]> CALCULATING TRAVEL COST

Travel cost is the average cost of traveling along a link. By default this is distance, i.e. the length of the link. However, you can define your own cost units, using for example the average time in minutes that it takes to traverse the link based on average speed along the link, or cost units expressed as fuel consumption, or any other cost units.

The easiest approach is to use average travel time. For this you need to know the speed limit for each link and then you must calculate the time it takes to traverse each link.

Take a look at the attribute table for the road theme. Notice a field called Road code. In this case the values 1 through 4 correspond to freeway, major road, residential road, and minor residential road. A detailed scrutiny reveals some inconsistency in the coding, but we disregard that in this exercise. Somewhat simplified we can assume that the average speed is, say, 50, 35, 25 and 15 mph for the above types of road codes. Based on this and the information in the Length field, we can calculate the average time it takes to traverse each link:

Make the road theme active and open the attribute table,
Theme > Table

Make the table editable:
Make the table active,
Table > Start Editing
Edit > Add Field, Call the field mph > OK
Edit > Add Field, Call the field minutes > OK

For more information on how to name the cost field, see Help. You may use hours, seconds or any other accepted name.

Use the Query Builder to select the links with the same Road Code values:

Make the table active,
Table > Query

Double-click Road_code, then click =, then double-click the desired value, click New Set

With the desired records now selected, Click the mph field in the attribute table (top of the column) to select it, then
Field > Calculate

Enter the chosen speed limit, click OK.
Repeat this process for the other road codes until all links have a speed limit.

Clear selected records, Edit > Select None.

Click the minutes field (top of column),
Field > Calculate

Enter the appropriate formula for converting line length and speed limit to travel time for a link > OK

Table > Stop Editing

You can now perform network analysis with travel time as cost units. You can set this in the Properties menu when solving Find Best Route or Find Nearest Facility or Find Service Area. However, you still need to set directions and turns, as well as match adresses.

Your network is still a free-flow network without any directional restrictions. In order to set directions, you need to add a field called oneway to the road theme attribute table. Use same procedure as above.

To set a direction, the field oneway must contain the value ft (from-to) or tf (to-from). ToFrom [...]]]> DEFINING DIRECTIONS

Your network is still a free-flow network without any directional restrictions. In order to set directions, you need to add a field called oneway to the road theme attribute table. Use same procedure as above.

To set a direction, the field oneway must contain the value ft (from-to) or tf (to-from). ToFrom or FromTo here correspond to the topological ordering as mentioned previously.

Use the table edit procedures as outlined above to create the oneway field, Click the Edit icon , then click the cell you want to edit, enter your value, hit Enter. Remember to save your edits, Table > Stop Editing, when done.

Make sure that on/off -ramps and freeway lanes are modeled with correct directions. This can be a tedious process, but nevertheless part of any QA/QC. Unless you want to spend endless hours in the lab, assume that everything is correct, then solve some routing in the vicinity of freeways and visually check that the route takes the lane/ramp it is supposed to. Edit as you go along.

If you want to restrict travel totally, enter n in the oneway field.