Core Skills in Graphical Construction and Presentation

Choose a graph that answers the geographical question

A graph turns a collection of values into a visual comparison. Its usefulness depends on choosing a form that matches both the data and what you want to communicate. Comparing traffic counts at different sites is a different task from showing how temperature changes through a morning.

First consider the data. Quantitative data are numerical measurements or counts; qualitative data are descriptions or categories. Qualitative responses can be grouped and counted: answers such as ‘satisfied’ and ‘dissatisfied’ can become numerical totals for a chart.

Numerical data may be discrete, such as a count of vehicles, or continuous, such as temperature, which can take values between whole numbers. This distinction helps you choose a suitable presentation.

For a pie chart, the categories must belong to the same whole. For a scatter graph, both measurements must refer to the same observation or site. Simply having two lists of numbers does not make them suitable paired data.

Build clear axes and sensible scales

An axis scale tells the reader what a distance along an axis represents. Equal distances must represent equal numerical changes. For example, labels of 0, 2, 4, 6 and 8 belong at equally spaced positions; labels of 0, 2, 5, 6 and 8 do not.

Before drawing, find the smallest and largest values. Choose a scale that includes every value, uses the available space well and is easy to plot accurately. Steps of 1, 2, 5 or 10 are often convenient, depending on the range. A very large range can squeeze small differences into an unreadable space, while a cramped scale may leave some values off the graph.

Label each numerical axis with the variable and its unit, such as ‘River depth (cm)’. On a bar graph, the category axis instead names the groups being compared. A graph title should identify what is shown and include the place or period where relevant.

Scales also affect the impression a graph gives. Starting a vertical axis close to the smallest value can make a modest change look dramatic. A zero baseline is particularly important for ordinary bar graphs because readers compare bar lengths. If a line graph uses a shortened numerical range, its starting value must remain clear.

Construct a line graph step by step

Consider these invented practice data, representing temperature at a fictional observation site during one morning. They are not recorded fieldwork results.

A line graph is suitable because temperature is a continuous measurement and the purpose is to show change over time. Put elapsed time on the horizontal axis and temperature on the vertical axis.

Use a horizontal range from 0 to 4 hours, with equal one-hour intervals. The graph below uses a vertical range from 8 to 13°C, labelled every 1°C. This includes every temperature, with 13°C on the top gridline. The vertical axis starts at 8°C, not zero, so the changes appear more pronounced than they would on a scale starting at zero. A value between labelled marks, such as 10.5°C, would be plotted halfway between 10°C and 11°C.

For the 11:00 reading, move to 2 hours along the horizontal axis, then up to the 13°C gridline, and mark the point. Repeat for each paired value. Join successive points in time order with straight line segments.

Data for Illustrative morning temperatures at a fictional observation site

The joined points make the rise and subsequent fall easy to see. They do not establish the exact temperature at every moment between readings: those intermediate temperatures were not measured. This same construction method transfers to genuine fieldwork data, using their actual times, values and units.

Make the graph communicate without guesswork

A reader should be able to understand a graph without needing you beside them. Include a specific title, readable labels, units and a clear scale. If colours, symbols or multiple lines represent different groups, provide a key. Choose styles that remain distinguishable rather than relying on several similar colours.

An annotation adds a short note to a relevant feature. On the practice graph, ‘Highest recorded temperature: 13°C at 11:00’ could be placed beside the highest point with a leader line. It identifies exactly what the reader should notice. An unsupported claim such as ‘temperature fell because cloud arrived’ would go beyond the data.

Keep the presentation uncluttered. Too many pie-chart categories produce narrow sectors that are difficult to compare; too many lines can become hard to follow. Select the detail needed for the geographical question, but do not remove inconvenient values merely to create a smoother pattern.

Finally, check the completed graph against the original values. Confirm that every point or bar is correctly positioned, labels and units are present, and the title accurately describes the data. Attractive presentation cannot compensate for inaccurate plotting.