Scale
Scale is arguably the most important, and scale information of some sort should be included on every map. The common way of doing this is by using a scale bar. Sometimes implicit information is satisfactory. A map of Australia, or any state of Australia, published for use in Australia does not need a scalebar as the scale information is implicitly known to the user, but published in an international atlas a scale would be required.
The first three are so important in map interpretation that they will be covered in the second module.
The source of the data and the date of publication are important pieces of information which can be used by the user to judge the quality of information provided by the map and its reliability. On a topographic map the data source(s) and publication date are usually included in the key area. In an atlas, the data sources and dates, may be described in an introduction. With a thematic map included with a report, the source may be described in the body of the report, but not in association with the map itself though it is preferable to place this information in the caption.