Meena wants to show diagrammatically how two sets of data, namely, population size and number of services are related to each other. Which one of the following will be the most suitable for the presentation?
- (a)Pie chart
- (b)Scatter graph
- (c)Bar chart
- (d)Triangular graph
Correct — B, Scatter graph. What Meena has is two measured variables for the same set of places — population size for each settlement and the number of services in it — and what she wants to show is how one moves with the other. That is exactly the job of a scatter graph: one variable on the horizontal axis, the other on the vertical, one point plotted for every settlement, so that the pattern of the cloud of points reveals whether services rise with population, how tightly, and which settlements sit far off the trend. Settlement geography uses this plot constantly, because the relationship between the size of a place and the range of services it supports is one of the standard findings of the subject, and outliers on the plot are themselves the interesting cases.
- (a)Pie chart — A pie shows how a single total divides into parts. It cannot express a relationship between two separate measurements, because there is no second axis to carry the other variable.
- (c)Bar chart — Bars compare the size of one variable across categories. You could draw population by settlement, or services by settlement, but the reader would have to hold two charts side by side and infer the link rather than see it.
- (d)Triangular graph — A triangular graph plots three components that together add up to a hundred per cent — employment split between primary, secondary and tertiary sectors, for instance. There are only two variables here, and they are counts, not shares of one total.
Choosing a graph is really choosing a question. Proportions of a whole call for a pie or a divided bar; magnitudes across categories call for bars; a three-part composition calls for a triangular graph; and the relationship between two measured variables calls for a scatter plot, on which a line of best fit and a correlation coefficient can then be laid.
Read the stem for the phrase 'are related to each other' and the answer is already decided — the word 'related' is the signal for a plot with two axes. The bar chart is the tempting wrong answer because bar charts are the default for anything with numbers, but a bar chart of population and a bar chart of services are two separate pictures and the reader has to do the comparing. On a scatter graph the comparing has already been done by the plotting. Two habits are worth building here: put the variable you think is doing the explaining on the horizontal axis, and look at the points that lie away from the general pattern, because in settlement studies those are usually the places worth a second look.
- A scatter graph plots paired values of two variables, one point per case, to show how they vary together.
- The pattern of points shows the direction and strength of the relationship, and a line of best fit can be added.
- A pie chart shows the division of a single total into parts and carries only one variable.
- A triangular graph plots three components that sum to 100 per cent and needs all three to be shares of one total.
- In settlement geography the size of a place and the number of services it supports are a standard pair for scatter plotting.
Match the data structure to the diagram: shares call for a pie, categories for bars, a three-part composition for a triangular graph, and a relationship between two measured variables for a scatter plot.
- Defaulting to a bar chart for any numerical comparison, when the question asks about a relationship.
- Using a pie chart for two variables; a pie can only divide one total.
- Reaching for a triangular graph whenever three things are mentioned — it needs shares of a single total, not any three numbers.
As a short applied scenario naming two or three variables, where the task is to pick the diagram that fits the data structure.
No directly related past PYQ was found.
- practice — not a real PYQ
The proportion of a district's workforce in the primary, secondary and tertiary sectors is best shown on which one of the following?
- (a)Scatter graph
- (b)Triangular graph
- (c)Line graph
- (d)Isopleth map
Answer(b) Triangular graph — it is designed for three components that together account for 100 per cent of a total.
- practice — not a real PYQ
On a scatter graph drawn to study whether rainfall influences crop yield, rainfall should normally be plotted
- (a)on the vertical axis, as the dependent variable
- (b)on the horizontal axis, as the independent variable
- (c)as the radius of proportional circles
- (d)as a sector of a pie chart
Answer(b) on the horizontal axis, as the independent variable — the variable doing the explaining goes on the horizontal axis and the one being explained on the vertical.