Multimodal Analysis Using Network Analyst

Outline Summarizing accessibility Summarizing accessibility Adding transportation modes to a network Adding transportation modes to a network Linking transportation networks Linking transportation networks

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

Example 1: Summarizing Accessibility Goal: find overall population within 1 hour of Albacete by current rail network Goal: find overall population within 1 hour of Albacete by current rail network Ignoring within-city accessibility issues for now Ignoring within-city accessibility issues for now General Method General Method 1. Create a service area of 1 hour from Albacete along current rail and export as a polygon 2. Select city points based on exported polygon 3. Summarize attributes of selection city points

Summarizing Service Areas, Part 1 1. Set service area analysis preferences 1. Layer Properties->Analysis Settings Impedance: Hours (Hours) Impedance: Hours (Hours) Default Breaks: 1 Default Breaks: 1 2. Polygon Generation Polygon Type: Detailed Polygon Type: Detailed Trim Polygons: checked Trim Polygons: checked – Value: 1 mile 2. Create a service area of 1 hour from Albacete along current rail – Click Network Analyst Toolbar -> Solve button 3. 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

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

Summarizing Service Areas, Part 3: Attributes of Selected Points Simplest Simplest Open attribute table Open attribute table Right mouse on Pop2005 column heading Right mouse on Pop2005 column heading Select “Statistics” Select “Statistics” Look at / copy and paste out “Sum” Look at / copy and paste out “Sum” More flexible More flexible Export attribute table data into new table Export attribute table data into new table Re-add summary table back into map document/layout Re-add summary table back into map document/layout Use 9.2 graphing functions (Attribute Table Options button- >Create Graph) Use 9.2 graphing functions (Attribute Table Options button- >Create Graph) Even More flexible… Even More flexible… Export using dbase file format, then open in Excel Export using dbase file format, then open in Excel Let’s you actually get a “bottom line” summary together with table Let’s you actually get a “bottom line” summary together with table

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

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

Creating Multimodal Networks In ArcGIS Network Analyst

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

Network Analyst Concepts 2 NA models connectivity relationships on top of topological relationships NA models connectivity relationships on top of topological relationships Topology Topology Deals with how things are connected Deals with how things are connected In ArcGIS, connections require a shared vertex In ArcGIS, connections require a shared vertex Connections must be snapped (close isn’t enough) Connections must be snapped (close isn’t enough) Connectivity Connectivity NA Only NA Only Depends on topological connections Depends on topological connections But can go beyond them (e.g.”no left turn” restriction) But can go beyond them (e.g.”no left turn” restriction)

Building Multimodal Network Datasets 1 Ensure that existing topology allows connections where you want them Ensure that existing topology allows connections where you want them In particular, look for lines crossing without a shared vertex In particular, look for lines crossing without a shared vertex To add vertices, two methods To add vertices, two methods Use Workstation Arc/Info command line clean/build Use Workstation Arc/Info command line clean/build Use linear referencing to add vertices along lines, then the “Integrate” command to snap things together. Use linear referencing to add vertices along lines, then the “Integrate” command to snap things together.

Building Multimodal Network Datasets 2 Set NA “Connectivity Policy” Set NA “Connectivity Policy” Default uses line end-points only Default uses line end-points only This causes “skipping” of roads connected to other roads at intermediate vertices This causes “skipping” of roads connected to other roads at intermediate vertices Switch to “All Vertexes” policy Switch to “All Vertexes” policy Create One Connectivity Group per Mode Create One Connectivity Group per Mode By adding “columns” By adding “columns” Make sure that your connection points span appropriate groups (in our case stations = rail and road) Make sure that your connection points span appropriate groups (in our case stations = rail and road)

Building Network Datasets 3 Multimodal Networks Require Connecting Points Multimodal Networks Require Connecting Points In our case, used rail stations In our case, used rail stations Since rail stations weren’t connected to road network, built connecting lines Since rail stations weren’t connected to road network, built connecting lines Add Connecting Line Segments between modal networks to ensure connections Add Connecting Line Segments between modal networks to ensure connections Manual Method – Use Editor Manual Method – Use Editor (precise but slow…) (precise but slow…) Automatic Method Automatic Method Requires ArcScript (arcscripts.esri.com) Requires ArcScript (arcscripts.esri.com) “AutoAddLines” “AutoAddLines” Input station points, roads network Input station points, roads network Outputs new lines from station points to closest road Outputs new lines from station points to closest road Not perfect since closest isn’t always correct – see Alabcete station Not perfect since closest isn’t always correct – see Alabcete station

Assignment Same as in-class exercise, but now using multimodal dataset Same as in-class exercise, but now using multimodal dataset Details on Stella Details on Stella Due one week from today (Thursday) Due one week from today (Thursday) Can start in class and obtain help Can start in class and obtain help Can work in groups if you like, but be clear on turn-in who is in a group Can work in groups if you like, but be clear on turn-in who is in a group Need to pick unique transit modes now… Need to pick unique transit modes now…