Necklace Map
A map where small glyphs — pie charts, bar charts, or symbols — are arranged along a curved “necklace” line that follows the outline of a geographic region, keeping each glyph near its actual location while eliminating overlap.
// 01 — The chart
What it looks like
A necklace map showing energy mix by province. Pie-chart glyphs are arranged along a curved necklace line that traces the country outline. Glyph size encodes total energy output; slices show fuel proportions.
// 02 — Definition
What is a necklace map?
A necklace map arranges small statistical glyphs — typically pie charts, bar charts, or proportional symbols — along a smooth curve (the “necklace”) that follows the outline of a geographic region. Each glyph represents a sub-region’s data and is positioned as close as possible to the sub-region’s actual location while being constrained to the necklace curve.
The key innovation is overlap prevention. Traditional symbol maps place glyphs directly on the map, which causes dense areas to collide. The necklace approach solves this by projecting every glyph onto a single ordered curve, preserving rough geographic proximity while guaranteeing that no two glyphs overlap — even when they vary dramatically in size.
Necklace maps are especially powerful for multivariate geospatial data: each glyph can encode multiple variables simultaneously (through slices, bars, or color), while glyph size encodes an aggregate quantity. The result is a compact, visually clean overview that would be cluttered on a conventional map.
Origin: The necklace map was introduced by Bettina Speckmann and Kevin Verbeek at Eindhoven University of Technology in 2010. Their algorithm optimally places proportional symbols on a closed curve while minimizing the displacement from each symbol’s true geographic position.
// 03 — Anatomy
Parts of a necklace map
// 04 — Usage
When to use it — and when not to
- You have multivariate data for sub-regions and need to show composition (e.g., energy mix, vote share) on a map
- Proportional symbol maps create too much overlap in dense areas
- You want to preserve rough geographic ordering while guaranteeing no glyph collisions
- Glyph sizes vary dramatically and would obscure each other on a standard map
- Your audience needs to compare compositions across regions at a glance
- You are mapping data for a single country or coherent geographic unit with clear sub-regions
- Precise geographic location is critical — glyphs are displaced from true positions
- Your data is univariate — a simple choropleth or proportional symbol map is cleaner
- You have many dozens of sub-regions — the necklace becomes too crowded to read
- The geographic region is not compact (long, thin, or fragmented territory)
- Your audience is unfamiliar with glyph-based maps — the learning curve is steep
- You need to show continuous spatial phenomena rather than discrete regional data
// 05 — Reading guide
How to read a necklace map
Follow these steps whenever you encounter a necklace map in the wild.
Identify the necklace curve and base region
The closed curve running around the map is the necklace. Inside or behind it you’ll see the geographic region (country, state) whose sub-regions are being visualized. Understand the spatial context first.
Read the legend for glyph encoding
Each glyph is a mini chart. Check what glyph type is used (pie, bar, bubble) and what each color slice or bar segment represents. Also check whether glyph size encodes a quantity (total population, GDP).
Compare glyph sizes around the necklace
Larger glyphs represent sub-regions with higher aggregate values. Scan the necklace for the biggest and smallest glyphs to quickly identify dominant and minor sub-regions.
Compare compositions within and across glyphs
Look at the internal breakdown of each glyph. Are certain categories dominant everywhere, or do proportions shift as you move around the necklace? Geographic patterns in composition are the key insight.
Use leader lines to locate sub-regions
If leader lines connect glyphs to points on the base map, follow them to understand which glyph belongs to which actual sub-region. Remember that positions on the necklace are approximate — not exact.
// 06 — Pitfalls
Common mistakes
Displacing glyphs too far from true positions
Fix: Use an optimization algorithm that minimizes total displacement. Add leader lines so readers can trace each glyph back to its actual sub-region on the base map.
Using too many categories in each glyph
Fix: Limit pie slices or bar segments to 4–6 categories. Tiny slices are unreadable at glyph scale. Group minor categories into an ‘Other’ bucket.
Encoding size by radius instead of area
Fix: Human perception compares areas, not radii. If you double the radius, the area quadruples, exaggerating differences. Always scale by area (radius ∝ √value).
Choosing a poor necklace shape
Fix: The necklace curve should roughly follow the region outline. A circle or ellipse works for compact regions; elongated territories need a custom curve that matches their shape.
Omitting the base map entirely
Fix: Without geographic context, readers can’t orient themselves. Always show at least a simplified outline of the underlying region so the spatial arrangement has meaning.
// 07 — In the wild
Real-world examples
European energy mix by country
Eurostat and energy agencies use necklace-style maps to display the electricity generation mix (coal, gas, nuclear, renewables) for each EU member state. Pie glyphs arranged around Europe’s perimeter make it easy to compare national portfolios without overlap in dense Western Europe.
Election results by district
Political analysts use necklace maps to show multi-party vote share across legislative districts. Each glyph is a pie chart whose size reflects total votes cast, with slices colored by party. The necklace layout prevents glyph collisions in urban areas with many small districts.
Agricultural output by province
The UN FAO has used glyph-on-curve layouts to show crop composition (wheat, rice, maize, other) for provinces within a country. Glyph size encodes total tonnes produced, and slices show proportions — revealing which provinces specialize in which crops.
// 08 — Quick reference
Key facts
// 09 — Variations
Types of necklace maps
Necklace maps vary primarily in the type of glyph placed on the curve and how the curve itself is shaped.
Pie-chart necklace
The most common form. Each glyph is a pie chart showing the composition of a variable (energy sources, vote share). Pie size encodes the total value.
Bar-chart necklace
Each glyph is a small grouped or stacked bar chart. Better than pies when precise comparison between categories is important.
Proportional symbol necklace
Simple circles whose area encodes a single variable. The necklace constraint solves the classic overlap problem of proportional symbol maps.
Open-curve necklace
Uses an open arc rather than a closed loop. Suitable for linear geographies like coastlines, river basins, or mountain ranges where a closed curve would be unnatural.
// 10 — FAQs
Frequently asked questions
What is a necklace map?+
A necklace map arranges small statistical glyphs — typically pie charts, bar charts, or proportional symbols — along a smooth curve (the "necklace") that follows the outline of a geographic region. Each glyph represents a sub-region's data and is positioned as close as possible to the sub-region's actual location while being constrained to the necklace curve.
When should you use a necklace map?+
Use a necklace map when you have multivariate data for sub-regions and need to show composition (e.g., energy mix, vote share) on a map. It also works well when proportional symbol maps create too much overlap in dense areas, and when you want to preserve rough geographic ordering while guaranteeing no glyph collisions.
When should you avoid a necklace map?+
Avoid a necklace map when precise geographic location is critical — glyphs are displaced from true positions. It is also a poor fit when your data is univariate — a simple choropleth or proportional symbol map is cleaner, or when you have many dozens of sub-regions — the necklace becomes too crowded to read.
Is a necklace map suitable for dashboards?+
Yes — a necklace map can work well in dashboards as long as the panel is large enough for readers to perceive the encoded values, has a clear title, and includes the legend or axis labels needed to interpret it.
What category of chart is a necklace map?+
Necklace Map belongs to the Geospatial family of charts. Charts in that family are designed to answer the same kind of question, so they often work as alternatives when one doesn't quite fit your data.
How do you read a necklace map?+
Start with the axis labels and legend, then look at the overall shape before zooming into individual marks. Compare prominent features against the rest of the data, and verify any conclusion against the underlying numbers when precision matters.