Choosing the right graph
Geographers use graphs to show data clearly and compare values at a glance. A multiple (compound) bar graph compares two or more sets of data side by side, a multiple line graph shows how several sets change over time, and a pie chart shows how a total is divided into parts.
Key idea
To find each pie-chart angle: angle = (value ÷ total) × 360°. The whole circle equals 360° and represents 100% of the data.
Multiple bar and line graphs
- Multiple bar graph: uses grouped bars with a key (legend). Good for comparing categories, e.g. rainfall in two towns each month.
- Multiple line graph: plots several lines on the same axes, each with its own colour or symbol. Good for showing trends over time, e.g. population growth of three states.
Both need a clear title, labelled axes, a suitable scale and a key so the reader can tell the data sets apart.
Example
If exports are worth RM90 out of a total of RM360, the pie slice = (90 ÷ 360) × 360° = 90°.
Drawing a pie chart
First find the total, then calculate each slice's angle using the formula. Draw the largest slice first, usually from the 12 o'clock position clockwise, and label each slice with its category and percentage. Pie charts are best when there are only a few categories; too many slices make them hard to read.
Remember
- Full circle = 360° = 100%.
- Angle = (value ÷ total) × 360°.
- Every graph needs a title, labels, scale and a key.
- Bars compare; lines show trends; pies show proportions.