Proportional symbol map
Thematic map using symbol size to represent quantitative data.
A proportional symbol map (or proportional point symbol map) is a type of thematic map that uses map symbols varying in size to represent a quantitative variable. Typically, the area of each symbol is mathematically proportional to the variable, though indirect methods such as categorizing symbols as 'small,' 'medium,' and 'large' are also used. This technique is generally applied to point symbols, distinguishing it from cartograms and flow maps, though gray areas exist between these types.
- field
- Cartography
- known_for
- Using symbol size to represent quantitative variables on thematic maps
Lore & Background
Arthur H. The technique was soon replicated and enhanced, including maps by W.
Reader's Guide
The proportional symbol map is significant for its intuitive visual encoding: larger symbols are interpreted as representing larger quantities, making it effective for ratio variables such as total population or agricultural production. Flannery found that Stevens's power law applies to circle area perception, leading to the Flannery Scaling Adjustment still used to correct underestimation. Since the early 1990s, GIS and graphics software have dominated production, and since 2005, interactive web maps have been enabled by platforms like Esri ArcGIS Online and CARTO. The technique complements choropleth maps by representing spatially extensive variables that are problematic for choropleths. Variables with negative values or qualitative categories are inappropriate, and high variance in data can cause overcrowding or invisibility of symbols.
Did You Know?
- Since the early 1990s, almost all proportional symbol maps have been created using GIS and graphics software.
Frequently Asked Questions
What is a proportional symbol map?
It is a thematic mapping technique in which the size of a point symbol on the map encodes a numerical value, so bigger symbols stand for bigger quantities. The symbol's area is typically scaled in direct mathematical proportion to the data value being displayed.
How does a proportional symbol map differ from a cartogram or a flow map?
Proportional symbol maps keep every geographic location fixed and only vary the size of discrete point markers, whereas cartograms reshape and resize entire regions to reflect values. Flow maps, in turn, encode quantities through the width of connecting lines rather than through symbol area.
Why are proportional symbol maps still a staple in cartography?
They let a reader compare magnitudes across many locations at a glance while preserving the underlying geography. The technique is simple to produce, easy to interpret, and adaptable to fields ranging from trade statistics to disease incidence.
More in Map Projections & Cartography Foundations 1-24
Elsewhere in the Map Projections & Cartography Foundations universe
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record