I am going to stick my neck out and define a map as a diagram which includes information about location, orientation and scale. Location because it is important to know where the map represents, orientation and scale so that we could use the map to navigate ourselves around it’s features or to determine the relationship between the features portrayed. This definition might include architectural plans for a new building, simple “how to find us” sketches as well as the highly detailed maps produced by national survey organisations.
It has to be noted that this tighter definition would fail to include one of the most famous maps in the world – the London Underground (Tube) system map. This map was originally designed by Harry Beck and has been rightly heralded as a design triumph. It clearly communicates with the transport system users and yet happily distorts both location and scale. The design concept has been copied by other city transport systems around the world.
To read the history of the tube map go to http://www.thetube.com/content/history/map.asp You can compare the original to the modern counterpart at http://www.thetube.com/content/tubemap/
A map has a purpose and that purpose is going to distort the representation. This is always true. A road map of a country has a specific purpose – to show a selection of roads, their general path and the junctions between them. The lines used to represent these roads have a width that does not obey the scale of the map – indeed in most instances it could not, if the line were to be drawn at all. We have grown used to the convention that map features are not drawn to the overall scale of the map although in most instances their relative position does conform to the scale.
For more on the inevitable distortions of maps take a look at the section titled Map Distortions or click one of the other links in our Maps and Mapping menu to the left of this page.