Choropleth maps work well for comparing rates, densities, percentages, and standardized indicators across provinces, cities, or counties. They should not let the physical size of a region stand in for the magnitude of a total.
What does the color mean?
Each region corresponds to one value. Values are divided into three to ten classes, then colored from light to dark or cool to warm. A legend must identify the indicator, unit, and class ranges so the reader can interpret the differences.
Density, growth, averages, and percentages usually fit choropleth maps. Totals such as population or revenue are affected by regional scale; proportional bubbles or per-capita values may communicate them more honestly.
Set labels and the legend before colors
Keep area names on when readers need to identify regions, and add value labels only when the map has enough space. The Legend switch controls both preview and export. Put the unit in the legend title, use a separate no-data entry, and reduce label density before increasing font size.
Four common classification methods
| Method | How it works | Useful when |
|---|---|---|
| Equal interval | Divides the full numeric range evenly | The range is meaningful and values are fairly even |
| Quantile | Puts a similar number of regions in each class | Every color should contain enough regions |
| Natural breaks | Finds relatively distinct groups inside the data | Exploration and skewed distributions |
| Logarithmic | Compresses differences in orders of magnitude | A few values are far larger than the rest |
No method is always best. Changing the method can change the apparent geographic pattern. When maps are compared or reused, state which classification method was used.
How many classes should you use?
Four to six classes are usually enough for screens and slides. Too few conceal variation; too many are difficult to distinguish from the legend. Start with five, then check whether most regions collapse into one class or any class remains empty.
How should you choose colors?
Single-hue sequential
Use this for indicators with a simple low-to-high order. Light for low and dark for high follows a familiar reading convention.
Multi-hue sequential
Cool-to-warm or blue-yellow-red ramps create stronger separation, but the sequence still needs to be obvious.
Diverging
Use two opposing colors when values move around a meaningful midpoint, such as positive and negative growth. All-positive data rarely needs a diverging ramp.
Missing data is not zero
Areas without data should use a separate light gray and be identified as “No data” in the legend. Treating blanks as zero turns absence into a false low value. EasyMap keeps numeric zero and missing values separate.
Check before export
- Does the title identify the place, indicator, and time?
- Does the legend include the unit?
- Does the color order match the numeric order?
- Can readers identify missing areas?
- Do dense labels remain readable?
- Does the classification fit the distribution?
Authoritative sources and further reading
- Data classification methodsPublisher：ArcGIS Pro Documentation
Compare three classifications
Use the same values with equal intervals, quantiles, and natural breaks, then compare both the legend and the spatial pattern.
Make a choropleth map →