Encyclopedias and atlases are important sources of information, so they can both be considered reference works. They can both be found in most libraries, and the information that they both contain tends to be quite general. However, there are several differences between the two as well.
Encyclopedias are reference works that provide summaries of all branches of knowledge. Although they are organized in a similar way to dictionaries, the entries of an encyclopedia tend to be much longer and detailed than those of a dictionary.
On the other hand, an atlas provides geographical information. It is a collection of maps or charts that are usually bound together. Although atlases can contain other types of information (pictures, data, facts about certain regions, etc.) the information is generally sparse and restricted to geography.