# Topological and Contiguous Accessibility

Accessibility can be measured in two different ways:

• Topological. Considers a system of nodes linked by transport infrastructures, implying discrete entities. In this case, accessibility is calculated at the nodal level and a function of the network structure. For seven nodes (a to g) located at an equal distance from one another, node d is the most accessible because it represents the minimal summation of total distances with all other nodes. Accessibility is measured only for nodes, while the intervening spaces are not considered outside the distance they represent.
• Contiguous. Considers a continuous space, here represented as a grid where each cell was assigned a level of accessibility. In this case, accessibility is a function of the spatial structure. Although accessibility values are here qualitative (ranking from least to most) a quantitative value can also be allocated for each cell.