A mostly red map: what it does not tell you about people
One color covering a huge area looks impressive, but people vote, fall ill or move, not land. Here is how to read that difference.
Short answer: the color that takes up the most space on a map is not necessarily the one that holds the most people. On maps that paint regions by result, rate or category, the drawn area weighs on the eye, but the population may be concentrated in small patches. Before concluding anything, ask how many people live in each painted region.
A story: Marta's map
Marta received on her phone the map of a fictional country, Alvorada, divided into two regions: Planalto and Litoral. Planalto is red and takes up about nine tenths of the drawing. Litoral, in blue, is a thin strip. The legend said only "result by region", and the message that came with the image claimed that "red won almost everything".
Marta went looking for the numbers. Planalto has 1 million inhabitants and Litoral has 9 million. If in each region the majority chose the color of its part of the map, blue represents nine out of every ten people in the country, even though it takes up only a strip of the drawing. The map was not wrong to show the area, but the phrase "won almost everything" treated land as if it were people.
What an area map does not answer
- How many people. Area and population are different measures, and an ordinary map shows only the first.
- How large the difference was. A region can get the same color with 51% or with 90%, and the color alone does not tell the two cases apart.
- What happens inside the region. A whole region gets a single color, even when it is divided on the inside.
How to re-read the map in four steps
- Note what the color represents. A result, a rate, a total or a category?
- Look up the population of each region. Use the source named on the map or an official statistics source.
- Compare area and population. If the larger region has far fewer people, the visual weight misleads.
- Look for an alternative version. A bar chart with the totals, or a map that resizes regions by population, often tells a different story.
Limits of this example
Alvorada, Planalto, Litoral and Marta are invented, and the numbers were simplified to illustrate the idea. In real life, the calculation depends on definitions, dates and sources. Not every map dominated by one color hides something: sometimes the area is exactly what matters, as in land-use maps. The goal is to pick the right measure for the question, not to distrust every map.