Graphical communication, charts and technical presentation
This domain tests the choice, construction and honest presentation of technical graphics: graphs, charts, tables, schematic and block diagrams, and layout of drawn information.
Choosing and constructing charts
- Line graphs show trends over a continuous variable; bar charts compare discrete categories; pie charts show composition of a whole; scatter graphs show correlation; histograms show frequency distribution of continuous data.
- Every axis carries a quantity and its unit, for example Time / s. Scales must be linear and evenly divided, and bar charts must start at zero to avoid exaggerating differences.
- Pie chart sector angle = percentage x 3.6 degrees, using values as a fraction of the total.
- Schematic and block diagrams use standard symbols; flow charts use the standard set of process, decision and terminal shapes.
- Use SI units and prefixes consistently, and report values to the precision the data justify.
Presentation
Drawings and charts need a title, a stated scale or key, labelled axes or balloons, and consistent lettering to ISO 3098. Tables carry column headings with units in the heading, not repeated in every cell. Layout should lead the eye from the general to the particular.
Worked example
A survey of 240 students: 90 travel by bus, 60 by car, 60 walk, 30 cycle. Percentages are 37.5, 25, 25 and 12.5. Multiply each by 3.6 to get sector angles of 135, 90, 90 and 45 degrees, which sum to 360 degrees and confirm the arithmetic.
Traps
Sectors that do not sum to 360 degrees; a truncated vertical axis on a bar chart; uneven scale intervals; missing units in tables; three-dimensional pie effects that distort sector area; a chart with no title or key.