Paper 3 · June 2023 · Settlement and Urban Geography
Which is a genuine disadvantage of using a departure from the mean bar graph to show ninety years of rainfall?
AIt requires the underlying data to be normally distributed before the bars can be plotted, and long rainfall records are almost never normally distributed, so the technique cannot lawfully be applied to them.
BIt hides the absolute totals and depends entirely on the base period chosen, so changing the years used for the mean changes every bar on the graph.
CIt cannot show years that were drier than average, since a bar has no way of representing a negative quantity.
DIt cannot show more than about ten years of record, because beyond that the horizontal axis becomes mathematically undefined.
Explanation
A reader sees only the departure, not the total, so a 20 per cent deficit could be 100 mm or 400 mm; and because every bar is measured from the mean, redefining the base period redraws the whole graph. Bars extend below the zero line perfectly well to show dry years, long records are exactly what the technique is for, and it makes no distributional assumption.
Derived from ZIMSEC Advanced Level Geography 6037/3 Paper 3 Practical Test, June 2023 session, Q5