Unlike indexes, abstracts provide brief summaries of the contents of the sources they cite. These summaries, or abstracts, are not intended to serve as a substitute for reading the cited sources, but rather to provide further guidance as to the contents of the sources, and their relevance to the information seeker.
General almanacs provide broad coverage both geographically and in terms of subjects covered.
Specialized almanacs concentrate on specific countries or regions, or particular topic areas. Almanacs are usually published annually. Atlases can cover the entire globe, or specific geographic regions. Bibliographies usually group together works by a particular author or on a particular topic. Bibliographies can appear at the end of books or articles to document sources used in the preparation of the book or article, or can be published as stand-alone informational sources.