A GIS-based Route Mapping Tool for Disabled Access in Urban ...

165The starting force was, as would be expected, always the highest recorded force forall surfaces. This measure is weight dependant. It was, however, found to be a veryimportant measure, with uneven surfaces causing the wheelchair to be slowed downand in some cases brought to a halt. The range of measured force was therefore acrucial measure, providing a good indicator for surface roughness. The results reflectedthe questionnaire and focus group responses.Dropped kerbs provide crossing points for wheelchairs across roads and consequentlyhad been identified as being extremely important to allowing movementaround an urban area. A total of nine factors were identified as being required to assessa drop kerb and included: height, surface, slope, camber, width, orientation,curvature, with bullnose and brickrunners. Collation of this information enabled acomprehensive and efficient method of ranking drop kerbs.The remaining urban features to be included in the digital database (e.g. the locationof steps, ramps and cambers) required only mapping by location, rather thanquantifying. Many of the urban features were gathered in the field, using a palmcomputer running ArcPad GIS. This provided an efficient method of mapping thedata and reduced the error that can often occur during data conversion.Initially, a network coverage representing pedestrian routes around the town centrewas derived using Ordnance Survey Land-Line data - an enhanced vector dataset, where features are represented as points and lines that are digitised and specificallycoded to show 37 layers. A number of issues arise when attempting to demarcatepavements as a range of different features defines pavement edges (e.g. buildingoutlines, walls, road edges). In order to provide consistency, pavement centrelineswere manually extracted using the Ordnance Survey Land-Line data as a backdrop.This removed the need to alter the original data whilst allowing the designer to uselocal knowledge to derive a network that best represented the general flow of pedestriansaround the town centre. Using the Dynamic Segmentation module inARC/INFO ® , linear measurements were used to define locations along linear features.All urban barriers were then associated with the correct measurement along theroute, defined as linear measures (e.g. pavement surface) or point events at measuredlocations (e.g. steps). The routes were assigned a direction along which the measurementsare made, thus, each route must be labelled twice since some of the barriersare direction dependent (e.g. slope). The drop kerbs were then stored as turntabledata, thereby allowing the direction of traverse to be significant. Storing the data usingdynamic segmentation means that the data is stored as a tabular database. Datacan be updated without altering the network topology.3. Model developmentMAGUS (Modelling Access with GIS in Urban Systems) is built entirely withinESRI ArcView ® GIS, using AVENUE programming language and Dialog De-Copyright © IGU/ISEP, Wien 2002. ISBN: 3-9500036-7-32504 EI P 906 I2 BealeL.doc 29.08.02