Large sailing ships have a lookout post, called a crow's-nest, on one of their masts. Why is the crow's-nest as high on a mast as possible.

To provide the best possible view

Explanation:

The crow's nest was located on the upper part of the main mast in a large sailing ship. It was so named because it is thought that Vikings used to carry crows in cages attached to the top of the mast and when they couldn't see anything they would let the crow out and follow its flight path.

It is located as high on the mast as possible so that it may provide the best possible view of what is ahead so that the ship can be able to navigate better. It was replaced by radar to a large extent.