Geography · Lesson 9

Statistical maps & diagrams, elementary surveying & GIS

JAMBWAECNECO

What the syllabus asks

JAMB: Practical Geography I D–F: statistical data, maps and diagrams; elementary surveying; GIS concepts, components, data sources, uses and problems in Nigeria

WAEC: statistical maps and diagrams; elementary surveying (chain and prismatic compass); Geographic Information System (GIS) (Nigeria)

NECO: statistical maps and diagrams; elementary surveying (chain and prismatic compass); Geographic Information System (GIS) (Nigeria)

What you will learn

Draw and interpret simple, compound and multiple bar graphs, line graphs and pie charts.
Calculate pie-chart angles and proportional-circle radii correctly.
Construct and interpret dot, choropleth, isopleth and flow maps.
State the advantages and disadvantages of each method.
Describe chain surveying, including offsets and the field book.
Use a prismatic compass to carry out open and closed traverses, and calculate back bearings.
Explain how to deal with obstacles in chain surveying.
Define GIS and state its components.
State sources of GIS data and its uses.
Explain the problems of GIS application in Nigeria.

Key points

Diagrams need title, key, scale, labelled axes and source.
Bar graphs: simple, compound (divided), multiple and percentage bars.
Line graphs show trends; climate graphs combine rainfall bars and temperature line.
Pie-chart angle = value/total × 360° (or % × 3.6).
Proportional circles: radius ∝ √value.
Dot maps: each dot a fixed quantity, placed where it occurs.
Choropleth maps shade areas by density or rate.
Isopleths join equal values: isohyets, isotherms, isobars.
Flow maps: line width ∝ volume.
Chain survey: chain, ranging poles, arrows, offsets, field book.
Obstacles: to ranging, to chaining, or to both.
Prismatic compass gives whole-circle bearings; back bearing = forward ± 180°.
Closed traverse allows calculation of closing error.
GIS components: hardware, software, data, procedures, people.
GIS problems in Nigeria: cost, skills, data, power, internet, awareness.

Start here: Statistical data and the rules of good diagrams

Geographers collect large amounts of numerical information: rainfall at a station each month, crop production in each state, population of towns, numbers of vehicles crossing a bridge. Raw tables of numbers are hard to read, so we turn them into statistical diagrams (graphs and charts) and statistical maps (which show where the values occur).

Types of statistical data

Primary data: collected by you in the field, e.g. a traffic count at a junction near your school, or rainfall read from your school’s rain gauge.
Secondary data: collected by others, e.g. NPC census tables, NiMet rainfall records, NBS reports.
Discrete data are counts (number of markets); continuous data vary smoothly (temperature).

Rules for every diagram (marks are given for these)

A clear title saying what, where and when.
A suitable scale on each axis (start at zero for bar graphs).
Labelled axes with units.
A key where colours or shading are used.
Source of data where known.
Neat, accurate construction with a ruler.

Choosing a vertical scale

Look at the largest value and the space available. If the largest value is 47 and you have 10 cm, 1 cm = 5 units gives 9.4 cm, which fits well.

Worked example 9.1 (illustrative data)

Daily traffic count at a junction: cars 240, buses 60, lorries 90, motorcycles 210. Choose a scale for a bar graph if 12 cm of paper is available.

Largest value = 240.
240 ÷ 12 = 20, so 1 cm = 20 vehicles is the minimum; choose 1 cm = 20 vehicles.
Bar heights: cars 12 cm, buses 3 cm, lorries 4.5 cm, motorcycles 10.5 cm.

Exam tip: When asked for “advantages” of a diagram, think of how easy it is to construct, read and compare; for “disadvantages”, think of space, exact values and how many categories it can show.

Continue this lesson in the free app →

Practice questions

1. A pie chart shows a sector of 25% of the total. Its angle is

90°
25°
45°
180°

Show answer

A: 90°
25% × 360° = 90°.

2. In a pie chart, crops worth ₦240 m out of a total of ₦960 m take an angle of

24°
240°
120°
90°

Show answer

D: 90°
240 ÷ 960 × 360° = 90°.

3. A map that uses different shades for different population densities in areas is a

isopleth map
flow map
choropleth map
dot map

Show answer

C: choropleth map
Darker shades show higher values.

4. A map with lines joining places of equal value (such as rainfall) is an

pie chart
isopleth map
choropleth map
pictogram

Show answer

B: isopleth map
Isohyets and isotherms are isopleths.

5. A map in which each dot represents a fixed number of people is a

dot map
choropleth map
flow map
isopleth map

Show answer

A: dot map
It shows distribution clearly.

Key words

Statistical data: Numerical information collected about a topic, e.g. rainfall, population, production.
Bar graph: A diagram using bars whose lengths are proportional to the values.
Line graph: A graph joining plotted points to show change over time.
Pie chart: A divided circle; each sector angle is proportional to its share of the total.
Pictogram: A diagram that uses symbols or pictures, each representing a fixed amount.
Dot map: A map where each dot stands for a fixed quantity, placed where it occurs.
Choropleth map: A map in which areas are shaded according to a density or rate.
Isopleth: A line joining places of equal value.
Proportional circle: A circle whose area is proportional to the quantity it represents.
Flow map: A map with lines or arrows whose width is proportional to the volume of movement.
Chain survey: Surveying by measuring straight lines (with a chain or tape) and offsets.
Offset: A short measurement at right angles from a chain line to a feature.

Learn Statistical maps & diagrams, elementary surveying & GIS step by step, free.
The Cara's Tips app teaches every topic from the very basics, with quick checks, worked examples and exam practice. It works offline.
Open this lesson in the free app Download for Android