All of the maps we have discussed briefly have something in common. They all have a definite set of rules that determine how the maps are made and what they all indicate. This is known as Specification. The specification must also contain all such information about the assumptions made in the map, all limitations and its information sources should also be mentioned.  This representation of information is called 'metadata' which is an important aid to those who read and interpret the maps. Single and stand-alone maps (like the maps with tourist resorts) are very simple to study.  While maps can have other extremes as well, like for series maps, the specification is much likely to be very complex because it is important that all these maps in the series should have similar content, as well as maintain consistency.