1. visualizing job accessibility with
GIS
linthicum plan 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

2. who lives where?
population available from 2000 Census tracts

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

4. jobs/housing balance
jobs to total population by Census tract

5. 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

6. 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 pp 4-7

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

8. job accessibility – by all modes
λ =

9. job accessibility – by automobile
λ =

10. job accessibility – by non-auto
λ =

11. 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

12. questions?