One example of the general principle formulated at the end of Section 10 is an ordinary ordnance survey map.

In the terminology of Section 2 the map as a whole is an icon. It serves as a metaphoric description of the terrain and employs various devices of ‘planned similarity’, e.g. a ‘bend in a road’ corresponds to a ‘bend in a line’ on the map.

However a map of this kind is also a metaphoric representation of time. I can use it to work out itineraries, not only so that I have a list of the places that I must pass through in order to get from locality A to locality B but also so that I can estimate the time interval that I shall experience in the process of doing so.

In these respects each map must be viewed as a unity, but the map as a whole can only be interpreted if we first make ourselves familiar with the mutual significance of several dozen conventional signs which are arranged on the paper in patterns.

All this is a complex process and, bearing in mind that the individual signs are not arranged in linear sequence like the individual letters on the typeface you are now reading, or the notes on a musical score, it may seem rather remarkable that we can read a map at all. Yet the making and reading of two dimensional maps is almost universal among mankind whereas the reading and writing of linear scripts is a special accomplishment associated with a high level of social and technical sophistication.

The explanation of this seeming paradox lies in what has already been said in Section 7.