Maps
Contiguous cartogram
Resizes regions by a data value while attempting to preserve shared boundaries.
- Map
- Geography
- Magnitude
What it answers
How do regional quantities compare after resizing geography?
- Shape
- Distorted connected regions
- What it shows
- Regional magnitude differences freed from land area.
Example
The question
How big is each region when sized by revenue instead of land area?
Regions resized by revenue (contiguous cartogram)
Illustrative data. It belongs to no company.
When to use it
Use it when
Showing totals while retaining approximate adjacency.
Avoid it when
When exact shapes or distances are required.
How to read it
Read labels and distorted region areas using a value key.
Note
Displayed area no longer means land area.
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
- Join region values to polygons and run a contiguous-cartogram transformation with stated constraints.
- Units
- State the mapped attribute unit, geographic level and boundary/coordinate reference. Rates need an explicit population or area denominator.
Worked example
RegionA value 60 and B40 getareas in ratio 3:2. Their displayed areas no longer show original land areas.
| RegionID | Value |
|---|---|
| R1 | 30 |
| R2 | 45 |