A NEW ALGORITHM FOR GRAPH-THEORETIC NODAL ACCESSIBILITY MEASUREMENT

Accessibility is a useful concept in the study of the spatial structur e of a region, if it can be calibrated appropriately. While graph-theo retic analysis has been used widely as a measurement scheme for the no dal accessibility in various transport networks, several limitations h ave been pointed out in the existing graph-theoretic accessibility mea surements. This study proposes a new algorithm for deriving the nodal accessibility measure, as an attempt to improve the conventional graph -theoretic accessibility measurements. Corrections are made in such a way that irrelevant loops are excluded and relevant indirect connectio n paths are included selectively. In particular, the new algorithm is developed for intraurban subway networks, and includes the characteris tics of intraurban subway traffic behavior. The concept of inconvenien ce of transfer is introduced, which is one of the most influential fac tors in the intraurban subway traffic. Nodal differentiation is allowe d, if the nodes play different roles in the travel behavior and eventu ally in the accessibility. For this purpose, we employ a weighting pro cedure, according to which the influence of transfer on a sequence of linkages is taken into account. The new accessibility measurement sche me is then applied to the Seoul subway network. Here GIS techniques ar e utilized to generate accessibility surfaces from the discrete nodal accessibility values, and the changes in the spatial structure of the nodal accessibility are analyzed. Finally, based on the resulting chan ges in the spatial structure of accessibility in the subway network, t he direction of changes in the land value and the land use pattern in Seoul is discussed.