Maps
Choropleth / filled-region map
Colours geographic regions by a numeric statistic to show spatial variation.
- Map
- Geography
- Comparison
What it answers
Where are regional values high or low?
- Shape
- Geographic regions filled by value
- What it shows
- Spatial contrasts and regional clusters.
Example
The question
Which regions have the most customers per 1,000 residents?
Customers per 1,000 residents by region, 2025 (choropleth map)
Illustrative data. It belongs to no company.
When to use it
Use it when
Spatial patterns in comparable regional rates or measures.
Avoid it when
Raw totals confounded with population or region area.
How to read it
Read geographic position and colour using the numeric legend.
Note
Rates or normalised measures are often preferable to raw totals.
The data you need
- Layout
- Attribute table plus geographic boundaries
- Fields
- RegionID: text; Value: number; matching polygon geometry or geographic boundary source
- One row is
- One region and its measured value. What is the grain?
- Rules
- Join data to boundaries with stable IDs. Declare geographic level, boundary version and coordinate reference system.
- Optional
- Names alone may be ambiguous. Geometry can be GeoJSON, a spatial file or a tool-supported boundary lookup.
- Preparation
- Validate the input grain and missing values. Join data to boundaries with stable IDs. Declare geographic level, boundary version and coordinate reference system.
- Units
- State the mapped attribute unit, geographic level and boundary/coordinate reference. Rates need an explicit population or area denominator.
Worked example
R1 rate 30/100=30%; R2 rate 45/300=15%. Shade byrate: R1 is higher althoughR2 has more events.
| RegionID | Value |
|---|---|
| R1 | 30 |
| R2 | 45 |