visualizing job accessibility with GIS linthicum plan512 July 2006 using Virginia as a subject area, in this presentation I will explain what accessibility is why it is important how I calculated it and how we can use ArcGIS to articulate the concept and analyze the results

who lives where? population available from 2000 Census tracts

who works where? job locations available by tract from 2000 CTPP

jobs/housing balance jobs to total population by Census tract

what does this data explain? job housing balance distribution density what doesn’t it explain? consideration of costs (travel time) access to jobs in other districts access to jobs by mode

what is job accessibility? accessibility – number of opportunities within a certain distance or travel time(1) O1 Ai – accessibility of zone I Oj – opportunities at zone j dij – distance between zones λ – friction factor O2 count the number of activity sites near home and then discount by the distance measure of the number of potential destinations (jobs) available and how quickly they can be reached A1 O3 O4 (1) Hanson, Susan. “The Context of Urban Travel: Concepts and Recent Trends.” Geography of Urban Transportation, Third Edition, Susan Hanson and Genevieve Giuliano, Editors. New York: The Guilford Press. 2004. pp 4-7

how to calculate λ the interaction formula becomes plot/regress ln(I) vs ln(d) to calculate the slope λ All Modes λ = -0.404 Auto λ = -0.293 Non-Auto λ = -0.251

job accessibility – by all modes λ = -0.404

job accessibility – by automobile λ = -0.293

job accessibility – by non-auto λ = -0.251

accessibility analysis shortcomings treats everyone in a tract as if they have the same mobility does not consider temporal variations such as peak / non-peak travel requires significant amounts of data does not distinguish between voluntary and necessary travel

questions?