A cartogram is a form of topological map, i.e. one in which the shape, distance and direction are disregarded, but the relative position of places is retained. It is used when the aim of the map is to highlight some value, such as population or production of a commodity. The area of the country is drawn proportional to the value.
SAQ 3.6A

This shows you the gross national product of the countries of the world. The names of some countries are written in. An area key is necessary if any values are to be extracted at all, though such a diagram is more often used just for comparative purposes. Parts of the world are easily recognisable. But can you spot Africa? Australia? Italy?

According to this cartogram, what is the approximate GNP of the UK?