Methods of graphic representation 1 or diagrammatic representation 1 may be used to illustrate an argument. The data are represented in a figure 2, graph 2, statistical chart 3 or map 3. A schematic representation of the relationships between variables is often called a diagram 4, for example the Lexis Diagram (cf. 437). A graph in which one co-ordinate axis is graduated logarithmically and the other arithmetically is called a semi-logarithmic graph 5, though such graphs are often inaccurately referred to as logarithmic graphs 5. A true logarithmic graph 6 has both axes graduated logarithmically and is sometimes referred to as a double logarithmic graph 6. A frequency distribution may be represented graphically by frequency polygons 7 obtained by joining points representing class frequencies with straight lines, by a histogram 8, where class frequencies are represented by the area of a rectangle with the class interval as its base, by bar charts 9, in which the class frequencies are proportionate to the length of a bar or by an ogive 10 representing the cumulative frequency distribution. More...