On a choropleth map, each shade stands for a class, which is a range of values. A district in a class has some density inside that range, but the map does not say which.
This lesson belongs to population distribution and density. The skill sits beside comparing maps without confusing correlation and cause.
How do you read the legend?
Follow three steps each time. Find the shade, find the class it matches, then write the class as a range.
Check the unit in the legend title, for example people per km². Check whether the top class is open, such as “1 000 and above”.
Worked example: two districts, one class
This is an original legend with four classes, in people per km².
| Shade | Class | What it proves |
|---|---|---|
| Lightest | 0 to 99 | Fewer than 100 per km² |
| Light | 100 to 499 | At least 100, below 500 |
| Dark | 500 to 999 | At least 500, below 1 000 |
| Darkest | 1 000 and above | At least 1 000, no upper limit |
Districts A and B are both in the light class. A reader who writes “A has 300 and B has 300” is guessing.
In fact A could be 110 and B could be 490. Then B is about 4.5 times denser than A (490 ÷ 110 = 4.45), yet both sit in one class. So the safe statement is that both are between 100 and 499.
The mistake that costs marks
The common slip is to treat the middle of a class as the real value, or to rank districts inside the same class.
- Wrong: “District M has 750 per km².” The legend gives 500 to 999.
- Right: “District M has a density between 500 and 999 per km².”
- Wrong: “District A is denser than District B” when both are in one class.
- Right: “Districts A and B are in the same density class.”
A comparison is safe only when the classes do not overlap.
Check yourself
Using the legend above, District M is in the dark class and District N is in the darkest class. Decide whether each statement is safe: (a) “N is denser than M.” (b) “N is twice as dense as M.”
Answer
(a) Safe. Every value in the darkest class is at least 1 000, and every value in the dark class is below 1 000.
(b) Not safe. M could be 950 and N could be 1 000, which is only slightly denser. Or M could be 500 and N could be 3 000. The legend cannot tell you the ratio.
What to study next
Put the legend skill into a full explanation with explaining a distribution pattern with more than one factor. Then test yourself on the density practice set or the map and graph reading practice.
If you want a teacher to check the wording of your map claims, see online one-to-one Geography tuition.