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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