Government 1009: Advanced Geographical Information Systems Workshop. LAB EXERCISE 3b: Network

Transcription

1 Government 1009: Advanced Geographical Information Systems Workshop LAB EXERCISE 3b: Network Objective: Using the Network Analyst in ArcGIS Implementing a network functionality as a model In this exercise, you will use Network analyst to find the closest fire stations from an address in the Dudley Street Neighborhood. (You could translate this to something similar with your own project location as well though this could be very time consuming and not worth it unless your final project has a network related objective). 1.0 Setting up your network 1. Open ArcMap. Start up ArcCatalog. 2. If the Network Analyst Extension is not enabled, on the Customize main menu, select Extensions and make sure Network Analyst is checked. 3. Copy the shapefile bostonstreets_project from the Gov1009\streetmap folder to your lab3b folder. Right-click the shapefile in TOC in ArcCatalog and select New Network Dataset. 4. This shapefile contains street data for Boston which has the same projection, coordinate system, datum, etc. as the rest of the massgis data. 5. I clipped this data from a larger dataset showing streets in the US: T:\ArcGIS Media Kit 10 for streetmap_usa. 6. The name of the network dataset is set to bostonstreets_project_nd by default. Click Next to continue. Network Connectivity defines how features that participate in a network connect to each other. The default connectivity for a network dataset places all sources in one connectivity group and assigns all edge sources endpoint connectivity. Accept the default connectivity, Click Next to continue. Earlier versions of ArcView GIS and ARC/INFO support optional elevation fields to establish connectivity. Each feature in a shapefile would be assigned two Z-elevation values, one for each endpoint. If the endpoints of line features have the same Z-elevation value, connectivity is established. If the values are different, they do not connect (e.g. in the case of bridges or tunnels). The elevation field contains logical elevation values for establishing connectivity only and does not provide height information for the feature. ArcGIS Network Analyst can use this data to modify the connectivity settings established in the previous step and will automatically search and map the relevant fields. If ArcGIS Network Analyst finds elevation fields data in your shapefile, it automatically chooses the Yes button and assigns the appropriate fields. ArcGIS Network Analyst supports turns in a shapefile based network. Turn information (such as turning restrictions and delays) enhance the quality of network analysis. Earlier versions of ARC/INFO and ArcView GIS used turn tables. These turn tables can be converted into turn features and used in the network dataset. By default Global Turns are selected. Global Turns are rules that can be set, such as all left turns have a delay of 15 seconds. Such a rule gives preference to right turning movements. The advantage of Global

2 Turns is that you do not need to create individual turn features for rules that apply to every turn in the network. 7. Click Yes to model turns in the network. Click Next to continue. Network attributes are properties of the network that are used to control navigation. Common examples are costs that function as impedances over the network. Restrictions like one-way are also examples of network attributes. The ArcGIS Network Analyst analyzes the source shapefile and looks for common fields like Meters, Minutes (FT_Minutes and TF_Minutes, one for each direction), and Oneway. If it finds these fields, it automatically creates the corresponding network attributes and assigns the respective fields to them. This dataset has Minutes and Meters calculated from the length of the arcs and the speeds allowed on the arcs. 8. Choose Minutes to calculate impedances. To use driving directions in a network analysis, they should be set in the network dataset. Select the default Yes. Also click yes to build the network. 2.0 Proximity analysis with networks In this section you will find the closest four fire stations (or schools) that can respond to a fire at a given address. You will also generate the fastest route from each of these fire stations (schools) that will be provided to each driver of the fire engine (or school bus). 9. If the Network Analyst toolbar is not already visible click main Customize, Toolbars, and activate Network Analyst. 10. The newly created network from the previous section bostonstreets_project_nd should be automatically added to your TOC. If not select it and select Yes to add the other elements associated with the network (edges, junctions and arcs for Boston s streets). To reduce the visual clutter un-check the network elements so that only the street arcs are visible. 2.1 Creating the Closest Facility analysis layer 11. On the Network Analyst toolbar, click the Network Analyst dropdown menu and click New Closest Facility. The Network Analyst Window now contains an empty list of Facilities, Incidents, Routes, and Barriers categories. Additionally, the Table of Contents contains a new Closest Facility analysis (group) layer. 2

3 12. Next you will add facilities from a point file for which a layer file has been created. Activate the Network Analyst window. Right-click Facilities in the Network Analyst window and click Load Locations. 13. Select Fire Stations (in Gov1009\massgis) from the Load From dropdown list. Leave the defaults on everything else on the window and then click OK. All fire stations in Massachusetts are eventually listed in the Network Analysis window and are displayed as facilities on the map. 2.2 Adding an incident Next, you will find a street address and add it as an incident for Closest Facility Analysis. 14. Right-click Incidents on the Network Analyst Window to select it as the feature layer to which you will add the street address as a network location. Select Find Address to bring up a new window. Enter an address in the Dudley Street Neighborhood, for example, 100 Dacia St, Boston MA in the text box. One location is found with that street address and is listed as a row in the table in the Find Dialog. 15. Right-click the row and click Add as Network Analysis Object This adds the located address as an incident on the Network Analyst Window and on the map. You can add other addresses in Boston if you want. 2.3 Closest Facility 16. Click the Analyst Layer Properties button next to Closest Facility on the Network Analyst Window to bring up the Layer Properties dialog. 17. In the Layer Properties dialog, click the Analysis Settings tab. Click the Impedance dropdown arrow and click Minutes (Minutes). Set the Default Cutoff value to 5. ArcGIS will search for fire stations that are within five minutes of the fire. Any fire station outside of five minutes drive time will be ignored. 18. Increase the Facilities to Find from 1 to 4. ArcGIS will attempt to search for four fire stations from the fire site, within the five minute cutoff. If there are only three fire 3

4 stations within the cutoff, then the fourth fire station will not be found. Under Travel From, select Facility (fire station) to Incident (fire). 19. Select Everywhere from the Allow U-Turns dropdown box. 20. Check the box labeled Ignore Invalid Locations. This will let you find the best route using located stops. Stops that were not located on the network will be ignored. 21. Also in the Accumulation tab of the Layer Properties select Minutes. 22. Click OK to save the settings. 23. Click the Solve button on the Network Analyst toolbar. The routes appear in the map and in the Route Category on the Network Analyst Window. Note that the number of fire stations found to be closest to the fire within the three minute cutoff will depend on your incident addresses. You can optionally increase the cutoff value to 4 minutes and see how many fire stations are found. 24. You can click the Directions Window button in the Network Analyst Toolbar to generate directions for routes from each fire station (This will only work if you have specified that you want to use driving directions while building the network). 2.4 Other functions in Network analyst 25. Service Area Polygons allows you to find the distance that can be reached from a facility within a specified amount of time. You can calculate 5 and 10-minute service area polygons for fire stations (or for libraries). You can also find out how much 4

5 population lies within each of these service areas by saving the polygons generated as a new shapefile and overlaying it with the Census data on population (by block, block group or tract). 26. You could create an Origin-Destination Cost Matrix for travel between different locations within Boston for example one could use the centroid of a census block group as the origin (and destination). Such a matrix can be used as an input for logistics, delivery, and routing analyses. 3.0 Implementing a Model (Optional) Recall, that model building is not only how we can replicate the spatial operations for future use but that it is also a way to document the transformations that will occur. You will now create a model that outlines exactly the same processes that you followed in section On the Standard toolbar, activate ArcToolbox. You can add a new toolbox and edit a new model as you did in previous labs. 28. Select the Make Closest Facility Layer tool in the Analysis Toolset of the Network Analyst toolbox in ArcToolbox and drag it into the model. Double-click the Make Closest Facility Layer tool in the model, to set properties. Select the Boston network as the Input Analysis Network in the dropdown list. In the Impedance dropdown list, click Minutes. See the screen for other parameters to set. 29. Next you will add the fire station locations (s) by using the Add Locations tool. Select the Add Locations tool in the Analysis toolset of the Network Analysis toolbox and drag it into your model window. Select the Fire Stations in Boston as the Input Locations with the Facilities sub layer. Keep the defaults for all the other parameters. Again drag in Add Locations (2) to your model window. Now add the incident.shp (a shapefile with one incident) as the input locations with the sub layer as incidents. 30. Select the Solve tool in the Analysis toolset in the Network Analyst toolbox and drag it into the model. Using the Add Connection tool, connect the output layer called Closest Fire Station (3) to the Solve tool. The Solve tool becomes yellow in color and the output 5

6 layer becomes green. Using the Select tool in the Model right-click on all the output layers and click Add To Display. This will add the final output to the map. 31. Save the model. From the Model menu, choose Run Entire Model to perform the analysis. Close the model to inspect the results. Click Yes, when prompted to save the model. The new route from the closest fire stations is added to the map. The route is also displayed on the map. (You can also optionally add the Directions tool as shown in the model diagram that follows). Model diagram for closest facility Question 1 (50 points) Implement one of the network analyst functions for your study area (new route, service area, closest facility or OD matrix). Attach a brief explanation and a screenshot of the final results of your analysis. (50 points) Attach screenshots of a model diagram and the final result of your analysis (20 extra points) 6