Look a little closer
On many world maps Greenland appears comparable to or larger than South America. In reality South America has more than eight times its area. The mismatch is not a surveying error but a consequence of projecting a round Earth onto a plane.
A sphere's skin cannot be flattened without stretching or tearing. Every world map therefore distorts some combination of area, shape, distance and direction. What it preserves depends on its purpose.
The Mercator projection draws longitudes as parallel vertical lines and latitudes as horizontal ones. On the globe, meridians crowd together toward the poles; keeping them equally spaced on paper greatly stretches east-west scale at high latitudes.
To preserve local shape and angles, north-south scale must expand by the same factor. Area distortion therefore accelerates toward the poles, enlarging high-latitude Greenland relative to South America nearer the equator.
This does not make Mercator simply wrong. A route following a constant compass bearing appears straight, which helped navigation, and its angle-preserving geometry works conveniently for zoomable web maps. It is poor for comparing world areas.
Equal-area projections improve size comparisons but stretch or squash shapes instead. No perfect flat world map exists, so readers should ask what a projection preserves and what it sacrifices.
