A symbol chart uses geometric symbols such as circles or squares, varying their size or color to represent quantities and categories. Symbols may be placed on ordinary axes or on maps. Bubble charts and proportional symbol maps are closely related forms.

Historical Background

Symbol-based visualization has roots in nineteenth-century cartography. Proportional symbols appeared on railway and thematic maps, and Charles Joseph Minard developed influential uses of symbol size for flows and quantities. Later work on area perception, including James Flannery’s scaling research, improved how proportional symbols are designed.

How to Read It

Read position first, then symbol size and color. Size usually represents magnitude; color may represent category or another quantitative value.

Design Notes

• Scale area, not diameter, when symbol size represents value.
• Provide a size legend.
• Avoid excessive overlap.
• Use color only when it adds meaning.

Summary

Symbol charts are flexible because they combine position, size, and color. They are useful for showing magnitude across locations or categories, but scaling and overlap require careful handling.