The Effects of Topography on Route Selection
The physical attributes of space, such as the topography, obviously influence the route selection process. Consequently, a route between two locations (1 and 3, also using the intermediate location 2) may use a path that is not necessarily the most direct. The detour index (direct distance divided by the transport distance) illustrates the importance of physical constraints on route selection.
| Route | Direct Distance (1-2-3) | Transport Distance | Detour Index |
| a | 20 km | 20 km | 1.0 |
| b | 20 km | 25 km | 0.8 |
| c | 20 km | 30 km | 0.666 |
Route (a) is shortest in terms of distance, but not necessarily the least expensive in terms of construction costs. Route (b) represents a tentative to reduce costs and this at the expense of a direct path. From a rational viewpoint, route (c) will be the one used to link locations 1 and 3. It offers the best compromise between the lost distance (indication of detour) and the supplementary construction costs imposed by construction over rugged terrain.