Transcript cost surface modelling

MEASURING
ACCESSIBILITY
USING
GIS
Rui Pedro Julião
Department of Geography and Regional Planning
New University of Lisbon
GeoComputation‘99
INTRODUCTION
Accessibility is a key issue
Traditional evaluation methods don’t
consider a real spatial model
Arc/Node logic versus Territorial logic
Accessibility measurement
Methodology
Lisbon and Tagus Valley Region
STARTING ISSUES
Graph Theory - Vector model
Continuous surface - Raster model
Geometry versus Analysis
3-step methodology:
1 - Data Acquisition and Integration
2 - Cost Surface Modelling
3 - Accessibility Analysis
DATA
ACQUISITION
AND INTEGRATION
Geographical information
Line weeding
Reclassification
Road Category
IP highway
IP 2 lane
IC highway
IC 2 lane
National Road
Regional Road
Municipal Road (former national)
Municipal Road
Level
41
21
42
22
23
24
25
26
COST SURFACE MODELLING
CCT 
P  60
TS  1000
CCT – Cell Crossing Time (min)
P – Pixel Size (m)
TS – Travelling Speed (Km/h)
Considering a 2-lane IP:
CCT 
P  60
100  60
6


 0.0750
TS  1000 80  1000 80
6 Km/h
network
outside
CCT = 1 minute
the
road
Road
Category
Average
Speed
Cell Crossing
Time (min)
IP highway
IP 2 lane
IC highway
IC 2 lane
National Road
Regional Road
Municipal Road
(former national)
Municipal Road
Off-road
110
80
110
70
60
55
0.0545
0.0750
0.0545
0.0857
0.1000
0.1091
50
50
6
0.1200
0.1200
1.0000
2 cost surfaces:
– With highways
– Without highways
ACCESSIBILITY ANALYSIS
COST SURFACE
ORIGIN
COST
DISTANCE
FUNCTION
ACCESSIBILITY
SURFACE
ALLOCATION
ACCESSIBILITY
TO THE HEAD OF
MUNICIPALITY
Cost surface calculation
without considering the
highway network.
ANALYSIS
WORKFLOW
Accessibility to head
of municipality and
territorial allocation
based on a cost
surface calculation
without considering
the highway
network
TERRITORIAL
ALLOCATION
Which territory should
belong to each
municipality according
to accessibility
measurement
ACCESSIBILITY TO
HIGHWAY NODES
ACCESSIBILITY
TO LISBON
Considering highways
and the other road
network
ANALYSIS
WORKFLOW
3-Step calculation:
a) estimate the travelling
time to each highway
node;
b) estimate the travelling
time and territorial
allocation for each
highway node;
c) add the travelling time
from Lisbon to the node
to its hinterland’s
travelling time
+ evaluation of
alternatives
CONCLUSIONS
Accessibility as key issue for many different studies



Methodological basis for accessibility measurement
GIS enables a full and dynamic territorial coverage
Future developments: Traffic data / Vehicle data
Barriers
Urban network data
Population density
Land use / Land cover