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Geography · Grades 9–12

Map projections, scale and spatial evidence

Representing a curved surface on a plane introduces distortion. Different projections preserve different properties and suit different tasks.

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Prerequisites

Relevant school subject foundations and careful reasoning.

Study notes

Projection

Representing a curved surface on a plane introduces distortion. Different projections preserve different properties and suit different tasks.

Scale

A representative fraction compares map distance with ground distance using matching units. Large-scale maps show a smaller area with more detail.

Aggregation

Regional averages can hide within-region variation. Changing boundaries can change summaries even when individual data do not change.

Interpretation

State data date, resolution, legend and missing coverage. A colourful map is not proof of a causal relationship.

Worked examples

At scale 1:50000, a map distance of 2 cm represents how many kilometres?

2×50000 cm=100000 cm=1 km.

1 km

Can every planar world map preserve all distances, areas and angles everywhere?

Flattening a curved surface entails tradeoffs.

No

Check your understanding

  1. Which describes a large-scale map?

    1. A map without coordinates
    2. Always a larger continent shown
    3. No scale denominator
    4. More detail over a smaller area

  2. Why should one avoid inferring individual behaviour from a regional average alone?

  3. A region has 400 people over 20 km². Find mean population density.

  4. Which metadata helps judge whether a map is current enough for a task?

    1. Only the font
    2. Only the number of colours
    3. The data date
    4. Only a decorative border

Answers and marking guidance

Answers and marking notes
  1. More detail over a smaller area

    A larger representative fraction generally means greater local detail.

  2. An aggregate can combine varied individuals and does not determine their separate characteristics. This is an ecological-inference risk.

    Credit aggregation versus individual inference.

  3. 20 people/km²

    400/20=20.

  4. The data date

    Changeable geographic data require temporal context.

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