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GIS Tools for Measuring Individual Accessibility in Real and Virtual Spaces

GIS Tools for Measuring Individual Accessibility in Real and Virtual Spaces. Harvey J. Miller Department of Geography University of Utah Salt Lake City, Utah USA harvey.miller@geog.utah.edu. eSI Visitor Seminar, National e-Science Centre, Edinburgh, Scotland - 06 September, 2007.

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GIS Tools for Measuring Individual Accessibility in Real and Virtual Spaces

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  1. GIS Tools for Measuring Individual Accessibility in Real and Virtual Spaces Harvey J. Miller Department of Geography University of Utah Salt Lake City, Utah USA harvey.miller@geog.utah.edu eSI Visitor Seminar, National e-Science Centre, Edinburgh, Scotland - 06 September, 2007 1

  2. Introduction • What is accessibility? • A multi-faceted concept • Individual’s ability to conduct activities • Shopping, education, health care, employment, recreation, socializing • Fundamentally spatial • Ability to be “present” at an activity location • Physical presence • Tele-presence 2

  3. Introduction • Why is accessibility important? • Accessibility is central to • Cities – compress lives in space & time • Transportation – physical access • Communication – info access • Accessibility in theory and application • Theory - Central to urban, transportation, social, economic theories • Application - Performance & social measures 3

  4. Introduction • Renaissance in accessibility measurement • Policy • Community livability (USA) • Social exclusion (Europe) • Resources, opportunities, social networks, social capital • GIS and geospatial technologies • Detailed geographic data • Spatial analysis, visualization • We need better accessibility tools • Not just better maps of old measures 4

  5. Outline of talk • Traditional accessibility measures • Place-based perspective • High mobility & connectivity • Individual accessibility: Theories and tools • Time geography • Enabling geo-spatial technologies • GIS tools for measuring individual accessibility • Network spaces • Multidimensional spaces • Virtual spaces • Locational privacy 5

  6. Traditional accessibility measures • Place-based methods • Distance • Spatial or temporal separation • Topological • Network connectivity • Attraction-accessibility • Spatial interaction & spatial choice • Benefits • Consumer surplus 6

  7. Traditional accessibility measures • People and place have become complex • A shrinking but shriveling world - Waldo Tobler • Transport costs have collapsed • But, relative differences are increasing • An accelerated world– James Gleick • Increasing mobility at all geographic scales • Activity organization is more complex • A fragmenting world- Helen Couclelis • Information and communication technologies (ICTs) • Activities are disconnecting from place and time 7

  8. Individual accessibility: Theories and tools • Time geography • Torsten Hägerstrand (1960s) • Spatio-temporal constraints on human activity • Types of constraints • Capability – physical needs, resources • Coupling – need to be coincident with others • Authority – fiat restrictions Lund, Sweden November 2001 8

  9. Theories and tools • Time geographic concepts • Types of activities • Fixed – e.g., home, work • Flexible – e.g., shopping, recreation • Stations • Locations and durations of activities • Space-time path • Individual movement with respect to time 9

  10. Theories and tools • Space-time prism • Accessibility to environment • Spatio-temporal region • Activities & resources within the region • Determined by • Space-time anchors • Fixed activities • Time budget • Min. required activity time • Max. travel velocity 10

  11. Theories and tools • Classical time geography - limitations • Uniform travel velocity • Simplifying assumption for tractability • Low-resolution • Lack of rigor in basic definitions, constructs • Cannot exploit new geospatial technologies & data • Physically-based theory • Does not handle information & communication technologies well 11

  12. Enabling geo-spatial technologies • Location-aware technologies (LATs) • Global Positioning System • Radiolocation • Inertial navigation • Location-based services (LBS) • Wireless Internet’s “killer app” • Information based on location in real time IBM Developerworks Library www-106.ibm.com/developerworks 12

  13. Enabling geo-spatial technologies • Space-time ecology • Where and when do people spend time? • Sensitive to social factors • Age/life cycle stage • Socio-economic status • Gender roles & household organization • Culture • LATs allow unprecedented, detailed analysis! African-American women Asian- American women Space-time paths in Portland, Oregon Mei-po Kwan, Ohio State University 13

  14. Enabling geo-spatial technologies • GIS • Mobile objects databases • Geosimulation • Agent-based modeling • High-resolution space-time data • Empirical and/or synthetic • Rethink theory and analysis of human behavior EpiSims: Individual-level simulation of disease propagation based on contacts in space and time episims.lanl.gov 14

  15. Individual accessibility in real and virtual spaces • Individual in space and time • Activity schedules and locations • Transportation resources and ICTs • Leverages geospatial science & technology • GIS, LATs, mobile objects, simulation • Accessibility in three spaces • Network – relax constant velocity assumption • Multidimensional – rigorous measurement theory • Virtual – relax physical space assumption 15

  16. Accessibility in network spaces • Transportation networks • Realistic paths and travel times • Linked to individual, network referenced activity schedules • Network time prism • Potential path tree (PPT) • Potential network area (PNA) PPT PNA 16

  17. Accessibility in network spaces • Dynamic networks • Travel velocity varies by location & time • Congestion • Activity timing • Other extensions • Multimodal networks • O’Sullivan et al. (2000) IJGIS • Cognitive/preference constraints • Kwan and Hong (1998) JGS Dynamic network PPT for SLC morning commute 17

  18. Accessibility in multidimensional space • Problems with time geography • No analytical statements of basic entities & relationships • Cannot support high resolution measurements • Query and analytical tool development • Specific to two spatial dimensions • Cannot link 1D (networks) and 2D • Cannot extend to 3D (natural space) 18

  19. Accessibility in multidimensional space • Time geographic measurement theory • Paths, prisms etc under perfect information • Finite but perfect instruments • Real world instruments are finite but imperfect • Theory properties • Information assumptions are explicit • Multidimensional space and time • Supports • Space-time query design • High-resolution measurement • Analysis of error & uncertainty propagation 19

  20. Accessibility in multidimensional space • Space-time path • Two major components • Control points - measured • Segments - unobserved • Perfect info assumption • Control points determine segments perfectly Recall: Classic space-time path 20

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  22. Accessibility in multidimensional space • Space-time prism • Temporally adjacent control points • Maximum velocity: Assumed or measured • Temporally disaggregate prism • Prism at time t • Intersection of simple objects in n - dimensional space Recall: Classic space-time prism 22

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  24. t 24

  25. t 25

  26. 26

  27. Past disc Disc intersection Future disc 27

  28. Accessibility in multidimensional space Simple geometric objects - easy to compute 28

  29. “Potential path ellipse” (aka PPA) 29

  30. Past disc Past disc & PPA PPA Future disc & PPA Future disc 30

  31. Accessibility in multidimensional space • Intersections • Path-prism intersections • Is a path or station within a prism at time t ? • Point in disc and/or ellipse problem • Prism-prism intersections • Do two prisms intersect at time t ? • Intersection of discs and or ellipses • n-disc case: Helly’s theorem Prism-prism intersection – Worse case in 2D 31

  32. Accessibility in multidimensional space • Example • Future and past discs based on network travel • Phoenix, Arizona USA 32

  33. Accessibility in virtual space • Virtual interaction • Accessibility to information and people using ICTs • ICT modes • Spatial constraints • Presence • Telepresence • Temporal constraints • Synchronous • Asynchronous Donald Janelle (1995) 33

  34. Accessibility in virtual space • New time geographic objects • Portal • A station that allows virtual interaction • A point location • A service radius • Examples: • Internet connection (point w/ zero radius) • WAP (point w/ positive radius) • Cell phone base station (point w/ positive radius) Spatial footprint of a portal A path and portals 34

  35. Accessibility in virtual space A path and portals 35

  36. Accessibility in virtual space • Message windows • Communication events • Defined by a portal and a time span • Send and receive windows • Two types • General: An actor interacting with a portal • Strict: An actual message 36

  37. Accessibility in virtual space • Virtual interaction constraints • Space • Easy! - Presence or not • Time • More difficult • Allen time predicates applied to message windows 37

  38. Accessibility in virtual space • Example: Who can receive a given message? • Synchronous • “Actor must interact with a portal during the entire message” • Asynchronous • “Actor must interact with a portal anytime after the message is sent” • Side conditions (not shown):- There must be enough time Sent message Possible receive window 38

  39. Locational privacy Random perturbation mask • Privacy protocols • Notify • Opt-in/out • Security & authorization • Build privacy into spatial representations • Spatio-temporal masking • Controlled noise into space-time trajectories Spatio-temporal weeding Scott Bridwell & Harvey Miller U of U Geography 39

  40. Conclusion • Traditional accessibility measures • Still important, but incomplete • High mobility and ICTs • Complex relationships between person, place & activities • Individual accessibility measures • Activities in space and time • Transportation networks • High-resolution measurement using LATs • Virtual interaction using ICTs • GIS tool development for accessibility analysis • Space-time activity queries, toolkits 40

  41. Conclusion • Future research • Synoptic measures • Aggregate accessibility patterns • Make sense of large space-time activity datasets • Imperfect measurement • Error propagation in time geographic queries • Applications: Theory and models • Accessibility-related phenomena • Travel demand, urban dynamics, social networks, social exclusion, epidemiology 41

  42. Questions? • Here and now? • or asynchronous telepresence? • harvey.miller@geog.utah.edu • Related papers (available at: www.geog.utah.edu/~hmiller) • 2007. “Place-based versus people-based geographic information science,” Geography Compass, 1, 503-535. • 2005. "A measurement theory for time geography," Geographical Analysis, 37, 17-45 • 2005. "Necessary space-time conditions for human interaction," Environment and Planning B: Planning and Design, 32, 381-401 . 42

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