Map projections

NASA Blue Marble satellite composite of Earth in an equirectangular global map. — NASA Blue Marble Next Generation, July 2004. A cloud-free satellite composite in a latitude–longitude grid: the map stretches high latitudes and is not equal-area.

A suggested lesson sequence

Use these stages at your own pace. Pause for students to sketch, compare observations or lead part of the demonstration.

01
Observe
Compare Greenland and Africa on the globe before flattening it. Predict which properties may change on the map.
Open Observe
02
Tinker
Flatten each projection fully. Compare the equal-sized circles at low and high latitudes, then describe the trade-off between area and shape.
Open Tinker
03
Explain
Choose a map use and explain which distortion would matter most for that purpose.
Open Explain
04
Check
Choose an answer and explain your reasoning. Each question includes feedback.
Open Check

Rehearse with the model

The same scene and controls as the lab. Load it when you are ready; use Start projector for the full classroom view.

Before the lesson

Compare how map projections represent a curved Earth on a flat surface, identifying the distortions each introduces.

Open the model before the lesson and choose a view that makes the important feature easy to see. Drag to rotate, and use the on-screen controls to change one variable at a time. The Controls panel explains the available keyboard shortcuts.

Ask students to predict the result before you change a setting. Compare the new view with the starting state.

Guide the demonstration

Compare Greenland and Africa on the globe before flattening it. Predict which properties may change on the map.

Flatten each projection fully. Compare the equal-sized circles at low and high latitudes, then describe the trade-off between area and shape.

Discuss a common misconception

“One flat world map can preserve every area, shape, distance and direction.” Flattening Earth’s curved surface necessarily introduces distortion. A projection may preserve a selected property, such as area, while changing others. Compare a map with a globe and choose its projection according to the task, rather than assuming all visual comparisons are equally reliable.

Build the explanation

A map projection transfers positions from a curved surface to a plane. Every projection distorts some combination of area, shape, distance and direction, so the right choice depends on the map’s purpose.

Flatten each projection fully. Compare the equal-sized circles at low and high latitudes, then describe the trade-off between area and shape.

Judge each projection when it is fully flat; intermediate shapes are a visual transition rather than a separate projection.

Teaching notes

Compare the properties a projection preserves with those it distorts before choosing it for a task.

Use the globe to check area comparisons, including the enlarged appearance of Greenland on a Mercator map.

Distinguish the requirements of a world map from those of a local map covering a much smaller region.

Check understanding

Open Check for 4 questions. Ask students to explain their choice before revealing the answer.

Return to the opening photograph. Ask students to identify one visible feature and explain which part of the model helps account for it.

Look more closely

Use these observations to connect the vocabulary to features students can identify.

Mercator

Read the definition

Equal-area

NASA Blue Marble satellite imagery displayed in a Mollweide projection with a graticule. — NASA satellite imagery reprojected by Strebe into Mollweide. This equal-area projection preserves relative areas but distorts shapes; the ocean has been lightened for legibility.