What are lateral marks based on in the IALA system?

In the IALA (International Association of Lighthouse Authorities) maritime buoyage system, lateral marks are specifically designed to indicate the sides of a navigable channel in relation to the observer's perspective. This means that the markings show whether the mariner should keep the buoy on the left or the right side when traveling into a harbor or up a channel.

The system is divided into two regions: Region A and Region B, each having its own color coding and shapes for the buoys. For example, in Region A, red marks are placed to the left side of the channel when entering, while green marks are on the right. This orientation helps ensure that vessel traffic can navigate safely and consistently based on the universally understood meaning of the lateral marks.

The other options do not pertain to the foundational principle of lateral marks within the IALA system. The tidal flow's direction does not dictate buoy placement; height and visibility of buoys are factors for ensuring safety and practicality, but they do not define what lateral marks represent concerning channel navigation.