Transport network extensions for accessibility analysis in geographic information systems

Abstract

In many developed countries high quality digital transport networks are available for GIS based analysis. Partly this is due to the requirements of route planning software for internet and car navigation systems. Properties of these networks consist among others of road quality attributes, directionality and turntables. In contrast in many so-called developing countries hardly any digital networks of sufficient quality exist for even the most basic GIS operations. It is not realistic to assume that on a short term high quality digital networks will become available. In such a case an airline network can be created. However this type of network assumes homogeneous space and does not take any physical obstacles into account. The Willowvale case is used to introduce the concept of (modified) Delauney networks that only creates airline links between physically neighboring locations. The purpose of this paper is twofold. First it is assessed to what extent ‘Airline’ and ‘Delauney’ based networks can be used as simplified cheap alternatives for the expensive digital road maps based on reality. The suitability of these alternative networks is examined in a Dutch case, where a detailed digital road map already exists. Results indicate that origin-destination distances computed with Delauney networks, when compared to airline distances, are much more in line with distances derived from the actual network. This leads to the conclusion that especially in heterogeneous areas the Delauney method offers an acceptable way of creating alternative road maps for the sole purpose of estimating the travel distance between locations. The ‘Dar es Salam’ case is used to illustrate that the method can also be applied when the road network needs to serve an urban area instead of linking small villages. The second purpose of the paper goes one step further and aims at getting insight into the sensitivity of accessibility outcomes when a Delauney network is used as a network extension to add more detail at the local level to an already existing digital road map. Results for the ‘Eindhoven’ case indicate that the addition of a more detailed lower scale network does indeed have a substantial influence on accessibility results