Geography · Lesson 19

Practical geography 4: statistical maps, diagrams and summary statistics

JAMBWAECNECO

What the syllabus asks

JAMB: statistical data, maps and diagrams. Calculation-focused companion to gg9.

WAEC: statistical maps and diagrams (bar graphs, line graphs, pie charts, proportional symbols, dot maps, choropleth, isopleth, flow maps), their construction, advantages and disadvantages and interpretation

NECO: statistical maps and diagrams (bar graphs, line graphs, pie charts, proportional symbols, dot maps, choropleth, isopleth, flow maps), their construction, advantages and disadvantages and interpretation

What you will learn

Calculate pie-chart angles and draw divided circles.
Calculate radii of proportional circles and squares.
Draw simple, compound and multiple bar graphs and climate graphs.
Construct dot maps with suitable dot values.
Calculate densities and choose class intervals for choropleth maps.
Interpolate isopleths between stations.
Draw flow maps with proportional widths.
Calculate and use mean, median, mode, range and percentage change.

Key points

Title, key, axes and units on every diagram.
Pie: value ÷ total × 360°, sum to 360°.
Proportional circles: r ∝ √value.
Compound bars show totals and components.
Climate graphs: rainfall bars, temperature line.
Dot value chosen so sparse areas get dots and dense areas stay readable.
Choropleth: density, graded shading, non-overlapping classes.
Isopleths by linear interpolation between stations.
Flow width ∝ volume, with a key.
Describe diagrams with figures and percentages.

Start here: Concept summary: statistics in the practical paper

Statistical maps and diagrams are part of the practical geography section of the syllabus. In WAEC Paper 3 they appear as one of the 15-mark optional questions (Question 1 being the compulsory map question), and JAMB asks objective items on choosing, drawing and interpreting them. A typical question gives a table of data and asks you to (a) draw a named diagram, (b) state its advantages and disadvantages, and (c) describe or explain what it shows. Every part has calculation marks, drawing marks and interpretation marks.

Unit gg9 introduced the types of diagram. This unit concentrates on the calculations and drawing techniques that the practical questions test: angles for pie charts, radii for proportional circles, dot values, densities and class intervals for choropleth maps, interpolation for isopleths, line widths for flow maps, and the summary statistics (mean, median, mode, range, percentage change) used to describe data. All data in this unit are illustrative (invented for practice, set in the fictional Oke-Ofa area); every calculation has been checked by computer.

Four rules for every diagram, worth marks in every scheme:

A title stating what, where and when.
A key (legend) for every colour, shading or symbol.
Labelled axes with units, or a stated scale for symbols.
Accurate plotting from your calculations, which you must show.

If a question says “show your working”, a table of calculations (for example, values → percentages → angles) earns marks even if the drawing has a small error.

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Practice questions

1. In a pie chart, a value that is 25% of the total gets an angle of

90°
25°
45°
100°

Show answer

A: 90°
0.25 × 360.

2. 450 out of 1,000 in a pie chart is

45°
150°
180°
162°

Show answer

D: 162°
0.45 × 360.

3. Proportional circles have radii proportional to the

square of the values
log of the values
square root of the values
values

Show answer

C: square root of the values
Area ∝ value.

4. If town B has four times town A’s population, its proportional circle radius is

the same
twice A’s
four times A’s
sixteen times A’s

Show answer

B: twice A’s
√4 = 2.

5. A choropleth map shows values by

shading areas
dots
lines of equal value
arrows

Show answer

A: shading areas
Density by area.

Key words

Pie chart: Circle divided into sectors proportional to parts of a total.
Proportional circle: Circle whose area represents a value; radius ∝ √value.
Compound bar: Bar divided into stacked components.
Climate graph: Rainfall bars with a temperature line for one station.
Dot map: Map using dots of fixed value to show distribution.
Choropleth: Map shading areas by ratio or density.
Isopleth: Line joining places of equal value.
Isohyet: Isopleth of equal rainfall.
Interpolation: Estimating values between known points.
Flow map: Map showing movement by bands of proportional width.
Primary data: Data collected first-hand by the researcher.
Median: The middle value of ordered data.

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