A map full of dark red areas can make a story feel obvious before you have read a single number. The colours may be accurate, yet the impression can still be misleading if you do not know what they measure.
Start with the legend. Does darker mean a larger total, a higher rate, a greater change or simply membership of a category? Those are different questions. A large population can produce a high count while having a comparatively low rate per person.
Read the gaps between the colours
Consider an invented map with bands of 0–9, 10–19 and 20–99. Two neighbouring areas valued at 19 and 20 receive different colours despite being close. Two areas valued at 21 and 90 share a colour despite being far apart. The bands are editorial choices that affect what stands out.
Look for their numerical boundaries rather than assuming equal colour steps represent equal changes. Also check whether the scale starts at zero, whether negative values have a separate colour and whether the map compares every area against the same baseline.
A blank area needs an explanation
White or grey can mean zero, no data, excluded territory or a value outside the selected period. It cannot safely mean all four. If the legend does not explain it, the map leaves an important question unanswered.
Next read the source and date. A map published today may use a survey from an earlier year. Administrative boundaries may also have changed, making a visual comparison with an older map less straightforward than it looks.
Before reposting, describe the actual claim in one sentence: “This shows reported cases per resident during this period,” for example. If you cannot finish that sentence from the title, legend and source, open the accompanying methodology. A useful map makes its measure legible; an arresting colour scheme alone does not establish the story.