Absolute and Relative Barriers

• Absolute barriers are geographical features that entirely prevent a movement. They must either be bypassed or be overcome by specific infrastructures. For instance, a river is considered as an absolute barrier for land transportation and can only be overcome if a tunnel or a bridge is constructed. A body of water forms a similar absolute barrier and could be overcome if ports are built and a maritime service (ferry, cargo ships, etc.) is established. Conversely, land acts as an absolute barrier for maritime transportation, with discontinuities (barriers) that can be overcome with costly infrastructures such as navigation channels and canals.
• Relative barriers are geographical features that force a degree of friction on a movement. In turn, this friction is likely to influence the path (route) selected to link two locations (A and B on the above figure). Topography is a classic example of a relative barrier that influences land transportation routes along paths having the least possible friction (e.g. plains and valleys). For maritime transportation, relative barriers generally slow down circulation such as straits, channels or ice.