Five questions before sharing a “true world map”

1. Which geometric property is preserved?

Read the projection name first. Equal Earth preserves relative area; Mercator preserves local angles; an orthographic globe shows one hemisphere. To judge a map’s “accuracy,” first decide which quantity you want it to represent accurately.

If the question is about country area, a screen full of land is not enough. If the question is about distance, an equal-area label does not solve it. Write the intended question in one sentence before choosing the view.

來源: Library of Congress · Geospatial reference data: projection properties

2. Are the display scales comparable?

Two country thumbnails can each be fitted to their own frame. That makes them readable, but it can make a small country look as large as a big one. A similar problem occurs when a screenshot is taken before and after changing the zoom.

For a visual area comparison, use a common scale and say so in the caption. If panels have independent scales, use them to compare detail or distortion patterns instead of absolute footprint. The caption should make this clear so readers do not mistake the illustration for an area comparison.

3. Are you comparing the center with the edge?

On the globe, a country near the edge is foreshortened and may be partly hidden. A small visible footprint does not establish a small territory. Center the relevant region and keep the zoom consistent before comparing outlines.

On a flat world map, the central meridian and seam also matter. A region split across the edges can seem widely separated even when it is continuous on the sphere. Name the view’s center if it is important to the comparison.

來源: PROJ · Orthographic projection

4. How detailed is the boundary source?

A world overview needs less detail than a harbour map. Natural Earth’s different source scales serve different uses, and enlarging the overview cannot restore every omitted island. Ask what source the author used, not only how many pixels the image contains.

Simplified boundaries are useful for learning and visualisation. The problem starts when an overview outline is presented as a precise official measurement without a method or qualification. Match the claim’s precision to the source’s purpose.

來源: Natural Earth · Dataset scales

5. What does the area number include?

Check whether the figure describes land area, surface area or an estimate from a displayed polygon. Water coverage and territorial coverage can change the answer. A unit such as km² is necessary, but it is not a complete definition.

Include the regions, projection, common scale, source and area definition when sharing a comparison. A short caption can give readers enough information to understand what the image shows and what it does not measure.

來源: World Bank · Land area: definition · World Bank · Surface area: definition

Common questions