Networks in GIS. Geometric Network. Network Dataset. Utilities and rivers One-way flow. Traffic data 2-way flow Multi-modal data

Transcription

1 Unit 6: Networks

2 Networks in GIS Model the flow of resources Consist of a set of connected centers or junctions (ArcGIS) displayed as points. Junctions are connected by links, or edges (ArcGIS) displayed as lines. Costs accumulate along edges, affecting the flow of resources.

3 Networks in GIS Geometric Network Utilities and rivers One-way flow Network Dataset Traffic data 2-way flow Multi-modal data

4 Network Analysis Route Selection What is the best route between 2 points? Calculated based on transit cost. The simplest cost calculations use segment length as the cost unit. Impedances along the route can also be modeled. Example: School Bus Routes

5 Figure from Bolstad, 2008 Route Selection

6 Network Analysis Resource Allocation Assigns network links to centers Uses similar algorithm to route selection Can be constrained by center capacity

7 Figure from Bolstad, 2008 Resource Allocation

8 Building a Network We will use Network Analyst to build a network dataset. The first required input is a layer representing the network links, such as a roads shapefile. Import this layer into a Feature Dataset This layer needs to topologically clean Planarized lines

9 Building a Network cont d. Create a new Network Dataset inside the Feature Dataset using the layer representing the network. This will create 2 feature classes, one called edges and one called junctions

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13 Create a Route Add Network Analyst toolbar Open Network Analyst window Add stops Add impedances Solve route

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15 Network Analysis Route and Optimal Route (Djikstra s algorithm) Service Area (Djikstra s algorithm) Closest Facility (OD Cost Matrix) (Djikstra s Algorithm) Location-Allocation Note: results of analyses in both maps and attribute tables!!

16 Input Data Network Dataset such as streets with travel time attribute

17 Closest Facility Identifies facility or facilities closest to an incident. An example might be hospitals within 5 minutes of schools, fire stations within distance of fires, etc. This could be used as part of an emergency management plan.

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22 Djikstra s Algorithm This is the solver used by the software to do routing, closest facility and service area analysis. orithm

23 Location-Allocation Graphic from ArcMap help files

24 Location - Allocation Complex type of network analysis. Used to select best locations for facilities from set of potential candidates. Can take into account the locations of existing (or competing) facilities.

25 Location - Allocation Example: Where should a manufacturing plant be located to minimize transport costs to retail outlets? (ArcMap Help) Retail outlets are the Demand Points Proposed mfr. Plant locations are Candidate Facilities Required Facilities are pre-existing (may be competitors) Analysis can be controlled with travel time attribute and number of candidates to be selected if desired.

26 Location-Allocation Inputs Slide 10 shows a location-allocation analysis with existing fire stations (required facilities). Analysis designed to locate new fire stations that will serve the most people within a given time.

27 Location-Allocation Inputs Demand Points Locations requiring services or goods, e.g., retail stores requiring inputs from factories; business customers; center of a zip code polygon weighted by number of people.

28 Location-Allocation The following slide shows an analysis with 56 demand points (uploaded from point layer), and 10 manually selected candidate facilities. Analysis parameters include choosing 4 facilities from the candidate locations.

29 Location-Allocation Map Output

30 Location-Allocation Table Output

31 Location-Allocation Problem Types Minimize impedance (default) Reduce transportation costs between warehouses and retail outlets. Maximize coverage Reach the most people in a given period of time (pizza delivery, EMS). Minimize facilities Same as maximize coverage, but number of facilities chosen by solver, not by user. Maximize market share Location influenced by presence and influence of competitors to maximize market share. Requires the most inputs including information about competitors.