Paper 3 · June 2023 · Settlement and Urban Geography
You are asked to show Zimbabwe's mean annual rainfall variations from normal for 1910 to 2000 on one diagram. Which technique is appropriate, and how is it constructed?
AA dispersion diagram: plot every one of the ninety yearly totals as a dot on a single vertical axis, so that the spread of the record, its median and its interquartile range can all be read directly from the column of dots.
BA departure from the mean bar graph: calculate the long term mean, plot each year's total minus that mean as a bar above or below a horizontal zero line representing the mean.
CA pie chart: convert each year's rainfall to a percentage of the ninety year total and draw it as a segment, so that wet years occupy the larger sectors.
DA scatter graph: plot rainfall against year and fit a best fit line, then read the correlation coefficient to measure how variable the record has been.
Explanation
The question asks for variations from normal, which is exactly what a departure from the mean or rainfall anomaly graph shows: bars above the zero line for years wetter than the mean and below it for drier years, so runs of dry years stand out at a glance. A superimposed running mean smooths the year to year noise. A pie chart cannot show departures at all, since it can only divide a whole into parts.
Derived from ZIMSEC Advanced Level Geography 6037/3 Paper 3 Practical Test, June 2023 session, Q5