Calculating Pie Chart Segments: To find the angle for a specific category, use the formula: . Each segment should be distinctively colored or shaded.
Constructing Radar Charts: Identify at least three variables and draw axes radiating from a central zero point. Plot the data points on each axis and connect them with lines to form a closed polygon shape.
Drawing Histograms: Ensure that the x-axis represents a continuous scale (e.g., time or distance). Bars must be of equal width and touch each other, as there are no gaps between continuous data intervals.
Pictogram Scaling: Select a simple, recognizable symbol and define a key where one symbol equals a specific quantity (e.g., 1 symbol = 10 people). Use partial symbols to represent fractions of that quantity.
| Diagram Type | Primary Purpose | Key Feature |
|---|---|---|
| Flow Line | Shows movement between places | Line thickness represents quantity |
| Desire Line | Shows general direction of movement | Simple straight lines on a map |
| Rose Diagram | Shows directional frequency | Radial axes based on compass points |
| Radar Chart | Compares multiple variables | Points connected to form a 'web' shape |
| Venn Diagram | Shows logical relationships | Overlapping circles for shared traits |
Flow Lines vs. Desire Lines: While both show movement, flow lines are precise and scaled by volume, whereas desire lines are simplified vectors showing only the start and end points of a journey.
Rose Diagrams vs. Radar Charts: Rose diagrams are strictly for directional data (like wind), while radar charts are used for comparing non-directional variables (like economic indicators or social factors).
Check the Key: Always look for a key or legend first. In pictograms and flow diagrams, the key is the only way to translate visual size or symbols back into numerical data.
Verify Axis Labels: For histograms and radial graphs, ensure the axes are correctly labeled with units. A common mistake is misinterpreting the scale of a radial axis.
The 'No Gaps' Rule: In exams, drawing a histogram with gaps between bars is a frequent error that results in lost marks. Gaps are for bar charts (discrete data), not histograms (continuous data).
Sum to 100%: When interpreting or drawing pie charts, always verify that the percentages add up to exactly 100% and the angles add up to .
Misleading Areas: In pictograms, if symbols are scaled by height and width simultaneously, the area grows quadratically, which can visually exaggerate the data difference. Always scale by one dimension or use multiple identical symbols.
Radial Distortion: In radar charts, the area of the resulting shape can be misleading because it depends on the order in which the axes are arranged. Focus on the distance from the center on each individual axis rather than the total area.
Flow Line Overlap: In complex flow diagrams, lines may overlap, making it hard to see individual paths. Use clear colors or offset lines to maintain legibility.
