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Multimodal Analysis

Multimodal Analysis. Using Network Analyst. Outline. Summarizing accessibility Adding transportation modes to a network Linking transportation networks. Summarizing Accessibility. General method adjust default “trimming” of service area calculations

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Multimodal Analysis

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  1. Multimodal Analysis Using Network Analyst

  2. Outline • Summarizing accessibility • Adding transportation modes to a network • Linking transportation networks

  3. Summarizing Accessibility • General method • adjust default “trimming” of service area calculations • Untrimmed gives large service area polygon • Basically, minimum convex hull • Some oddities at edges • Trimming shows areas near network • 1.6km trim might be U.S. max walking distance • Does not take into account stops • When visual isn’t enough… • Export service area polygon into separate file • Use this file for spatial selection, or overlay as appropriate

  4. Example 1: Summarizing Accessibility • Goal: find overall population within 1 hour of Albacete by current rail network • Ignoring within-city accessibility issues for now • General Method • Create a service area of 1 hour from Albacete along current rail and export as a polygon • Select city points based on exported polygon • Summarize attributes of selection city points

  5. Summarizing Service Areas, Part 1 • Set service area analysis preferences • Layer Properties->Analysis Settings • Impedance: Hours (Hours) • Default Breaks: 1 • Polygon Generation • Polygon Type: Detailed • Trim Polygons: checked • Value: 1 mile • Create a service area of 1 hour from Albacete along current rail • Click Network Analyst Toolbar -> Solve button • Export service area polygon • In main map table of contents, right mouse on Polygons layer inside Service Area Group • Select Data->Export and find it a home

  6. Summarizing Service Areas, part 2(Standard ArcGIS Point in Polygon Method) • Selecting Points in a Polygon • Add “Urban Areas” Spanish Urban Points 2005, if necessary • Main Menu Selection->Select by Location • I want to: “select features from” (default) • The following layers: “Spanish Urban Points 2005” • That: Intersect • The features in this layer: [your service area polygon name]

  7. Summarizing Attributes of Selected Points • Simplest • Open attribute table • Right mouse on Pop2005 column heading • Select “Statistics” • Look at / copy and paste out “Sum” • More flexible • Export attribute table data into new table • Re-add summary table back into map document/layout • Use 9.2 graphing functions (Attribute Table Options button->Create Graph) • Even More flexible… • Export using dbase file format, then open in Excel • Let’s you actually get a “bottom line” summary together with table

  8. Summarizing Service Areasversion 2 • Goal: to count only urban areas within walking distance of station • Presuming, for the moment, that walking distance is U.S. standard 0.25 miles (!) • Method • Use NA preferences “trim polygons” to control network buffering, or “no trim” for broad service region • Use standard map overlay functions to combine accessibility polygons with land cover, etc.

  9. Example Polygonal Overlay Based on Service Areas • Add “Urban Areas” to map • Calculate a service area polygon • Export that service area and add to map • Use “Intersect” command • Layer 1: service area polygons • Layer 2: existing urban areas • Output: urbanized polygons in service area

  10. Creating Multimodal Networks In ArcGIS Network Analyst

  11. Key Concepts • Network Analyst General Concepts • Start with line segments and nodes (normal line layer) • After “building” network dataset, have • Edges (2 per line segment, representing potential movement in each direction) • Junctions (topologically joining adjacent edges)

  12. Network Analyst Concepts 2 • NA models connectivity relationships separately from topological relationships • Topology • Deals with how things are connected • In ArcGIS, connections require a shared vertex • Connectivity • NA Only • Depends on topological connections • But can go beyond them (e.g.”no left turn” restriction)

  13. Building Network Datasets 1 • Ensure that existing topology allows connections where you want them • In particular, look for lines crossing without a shared vertex • To add vertices, two methods • Use Workstation Arc/Info command line clean/build • Use “Integrate” command

  14. Building Network Datasets 2 • Add Connecting Segments between modal networks to ensure connections • Manual Method – Use Editor • (precise but slow…) • Automatic Method • Requires ArcScript (arcscripts.esri.com) • “AutoAddLines” • Input station points, roads network • Outputs new lines from station points to closest road • Not perfect since closest isn’t always correct – see Alabcete station

  15. Assignment • Same as in-class exercise, but now using multimodal dataset

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