Maps
Proportional-symbol / bubble map
Places symbols geographically and scales their areas continuously with values.
- Map
- Geography
- Magnitude
What it answers
Where are quantities largest at point locations?
- Shape
- Located symbols with proportional areas
- What it shows
- Geographic concentration and magnitude.
Example
The question
Where are our largest stores by sales?
Store sales by town (proportional symbols, EUR million)
Illustrative data. It belongs to no company.
When to use it
Use it when
Showing totals without allowing land area to dominate.
Avoid it when
Severe symbol overlap or inaccurate locations.
How to read it
Read location, then symbol area from its legend.
Note
Scale area rather than radius.
The data you need
- Layout
- Long table
- Fields
- LocationID: text; Longitude,Latitude: numbers; Value: nonnegative number
- One row is
- One point location and its value or weight. What is the grain?
- Rules
- State CRS. For WGS84, longitude is [-180,180] and latitude [-90,90]. Validate coordinate order.
- Optional
- For unweighted density, each point may have weight 1. Project coordinates appropriately for distance calculations.
- Preparation
- Validate the input grain and missing values. State CRS. For WGS84, longitude is [-180,180] and latitude [-90,90]. Validate coordinate order.
- Units
- Symbol area uses a count or amount; coordinates use a declared CRS. A displayed share needs its own total.
Worked example
LocationsA30, B45 use circle-area ratio 2:3. Radius ratio is sqrt(30/45), not 30/45.
| LocationID | Longitude | Latitude | Value |
|---|---|---|---|
| A | 18.07 | 59.33 | 30 |
| B | 11.97 | 57.71 | 45 |