Gis tools for measuring individual accessibility in real and virtual spaces
Download
1 / 42

- PowerPoint PPT Presentation


  • 157 Views
  • Uploaded on

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 [email protected] eSI Visitor Seminar, National e-Science Centre, Edinburgh, Scotland - 06 September, 2007.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about '' - jamil


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Gis tools for measuring individual accessibility in real and virtual spaces l.jpg

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

[email protected]

eSI Visitor Seminar, National e-Science Centre, Edinburgh, Scotland - 06 September, 2007

1


Introduction l.jpg
Introduction Virtual Spaces

  • 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


Introduction3 l.jpg
Introduction Virtual Spaces

  • 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


Introduction4 l.jpg
Introduction Virtual Spaces

  • 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


Outline of talk l.jpg
Outline of talk Virtual Spaces

  • 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


Traditional accessibility measures l.jpg
Traditional accessibility measures Virtual Spaces

  • Place-based methods

    • Distance

      • Spatial or temporal separation

    • Topological

      • Network connectivity

    • Attraction-accessibility

      • Spatial interaction & spatial choice

    • Benefits

      • Consumer surplus

6


Traditional accessibility measures7 l.jpg
Traditional accessibility measures Virtual Spaces

  • 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


Individual accessibility theories and tools l.jpg
Individual accessibility: Theories and tools Virtual Spaces

  • 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


Theories and tools l.jpg
Theories and tools Virtual Spaces

  • 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


Theories and tools10 l.jpg
Theories and tools Virtual Spaces

  • 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


Theories and tools11 l.jpg
Theories and tools Virtual Spaces

  • 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


Enabling geo spatial technologies l.jpg
Enabling geo-spatial technologies Virtual Spaces

  • 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


Enabling geo spatial technologies13 l.jpg
Enabling geo-spatial technologies Virtual Spaces

  • 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


Enabling geo spatial technologies14 l.jpg
Enabling geo-spatial technologies Virtual Spaces

  • 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


Individual accessibility in real and virtual spaces l.jpg
Individual accessibility in real and virtual spaces 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


Accessibility in network spaces l.jpg
Accessibility in network spaces Virtual 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


Accessibility in network spaces17 l.jpg
Accessibility in network spaces Virtual 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


Accessibility in multidimensional space l.jpg
Accessibility in multidimensional space Virtual Spaces

  • 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


Accessibility in multidimensional space19 l.jpg
Accessibility in multidimensional space Virtual Spaces

  • 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


Accessibility in multidimensional space20 l.jpg
Accessibility in multidimensional space Virtual Spaces

  • 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


Slide21 l.jpg

21 Virtual Spaces


Accessibility in multidimensional space22 l.jpg
Accessibility in multidimensional space Virtual Spaces

  • 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


Slide23 l.jpg

23 Virtual Spaces


Slide24 l.jpg

t Virtual Spaces

24


Slide25 l.jpg

t Virtual Spaces

25


Slide26 l.jpg

26 Virtual Spaces


Slide27 l.jpg

Past disc Virtual Spaces

Disc intersection

Future disc

27


Accessibility in multidimensional space28 l.jpg
Accessibility in multidimensional space Virtual Spaces

Simple geometric objects - easy to compute

28



Slide30 l.jpg

Past disc Virtual Spaces

Past disc & PPA

PPA

Future disc & PPA

Future disc

30


Accessibility in multidimensional space31 l.jpg
Accessibility in multidimensional space Virtual Spaces

  • 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


Accessibility in multidimensional space32 l.jpg
Accessibility in multidimensional space Virtual Spaces

  • Example

    • Future and past discs based on network travel

    • Phoenix, Arizona USA

32


Accessibility in virtual space l.jpg
Accessibility in virtual space Virtual Spaces

  • Virtual interaction

    • Accessibility to information and people using ICTs

    • ICT modes

      • Spatial constraints

        • Presence

        • Telepresence

      • Temporal constraints

        • Synchronous

        • Asynchronous

Donald Janelle (1995)

33


Accessibility in virtual space34 l.jpg
Accessibility in virtual space Virtual Spaces

  • 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


Accessibility in virtual space35 l.jpg
Accessibility in virtual space Virtual Spaces

A path and portals

35


Accessibility in virtual space36 l.jpg
Accessibility in virtual space Virtual Spaces

  • 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


Accessibility in virtual space37 l.jpg
Accessibility in virtual space Virtual Spaces

  • Virtual interaction constraints

    • Space

      • Easy! - Presence or not

    • Time

      • More difficult

      • Allen time predicates applied to message windows

37


Accessibility in virtual space38 l.jpg
Accessibility in virtual space Virtual Spaces

  • 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


Locational privacy l.jpg
Locational privacy Virtual Spaces

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


Conclusion l.jpg
Conclusion Virtual Spaces

  • 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


Conclusion41 l.jpg
Conclusion Virtual Spaces

  • 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


Questions l.jpg
Questions? Virtual Spaces

  • Here and now?

  • 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


ad