The copyright holder is usually the author, but for travel guidebooks it is often the publisher.
The copyright clause determines who shall have the right to license copies of a book.
In the USA, copyright is created automatically upon creation of a work of art or writing, and copyright is vested in the creator of the work, who may license to others the right to make copies of the work.
most works of art (including books), the copyright
holder is the creator (author), but for many
series guidebooks, copyright is held by the
times a guide is originally written by an
author or authors, but revised by others.
A contract which gives the publisher copyright
is usually termed a "work-for-hire" contract,
because the author is working as a temporary/contract
employee; he or she is not considered to be
creating the work alone.
It's always good to get copyright if you can, but its value depends on the rights you retain after you've agreed to allow a publisher to publish your work.