Key Terms

📖 Key Terms

Choropleth map — a map that uses shading or colour intensity to show how a variable varies across different areas. Darker shading conventionally represents higher values. The map assumes values are uniform across each zone, which is a significant limitation.

Dispersion diagram — a graph that plots every individual data value as a dot on a vertical scale, grouped by location or category. Unlike a bar chart (which shows only a mean or total), a dispersion diagram shows the spread of the data — whether values cluster tightly or are widely scattered. A median line and inter-quartile range can be added.

Kite diagram — a specialised presentation technique for transect data. The x-axis shows distance along the transect; the y-axis is symmetrical above and below a centre line; the width of the "kite" at each measurement point shows the abundance or frequency of a species. Multiple species can be overlaid, making succession patterns visible.

Desire line — a straight line drawn on a map between an origin and a destination, showing the direction and relative volume of movement (the line width is proportional to the quantity of flow). Desire lines do not show the actual route taken — only the straight-line direction and volume of movement.

Isoline — a line on a map connecting all points with the same value of a measured variable. Contour lines are a familiar example (equal altitude), but isolines can represent any continuously varying quantity such as noise levels, temperature, or air pollution concentration. Isolines never cross; they must be labelled with their value.

Proportional circle — a presentation technique in which circles are drawn at locations on a map, with each circle's area (not radius) proportional to the value it represents. This means a location with twice the value of another should have a circle with twice the area — so the radius of the larger circle is only √2 (approximately 1.41) times the radius of the smaller one.

Scatter graph — a graph used to test whether a relationship (correlation) exists between two continuous variables. Each pair of measurements is plotted as a single point; the pattern of points reveals whether there is a positive, negative, or no correlation. A line of best fit can be added to show the overall trend.

Line of best fit — a single straight line drawn through the cloud of points on a scatter graph to show the overall trend in the data. It is positioned so that roughly equal numbers of points lie above and below it. It is NOT drawn from point to point — it represents the trend, not the path between measurements.

Positive correlation — a relationship in which two variables increase together. On a scatter graph, points slope upward from left to right. Example: as distance from the sea increases along a sand dune transect, soil depth tends to increase.

Negative correlation — a relationship in which one variable decreases as the other increases. On a scatter graph, points slope downward from left to right. Example: as distance from the cliff base increases, average pebble size decreases.

No correlation — a situation in which two variables show no clear relationship. Points on a scatter graph are scattered randomly with no clear slope. The line of best fit is approximately horizontal. Spearman's rs is close to 0.