16.5 3D Thematic Maps

Key takeaways

3D thematic maps extrude polygons or points by a data attribute.

Visually compelling but easy to mislead — occlusion, perspective distortion.

Modern web tools (deck.gl, MapLibre) make 3D mapping accessible.

Introduction

Since 2015 or so, 3D thematic mapping has exploded — extruded polygons on web maps, buildings rendered at true height, choropleths lifted into 3D prisms. They're beautiful, and occasionally useful. This short lesson covers when to use them and how.

Extruded choropleths

Instead of colour, represent a variable as polygon height:

Each polygon's colour still encodes one variable.
Its vertical extrusion encodes a second.
Bivariate visualisation in 3D space.

Example: county choropleth coloured by income, extruded by population.

Tools:

deck.gl GeoJsonLayer with extruded: true.
Kepler.gl 3D polygon visualisation.
MapLibre GL fill-extrusion layer.
QGIS 3D map view.

Extruded point data

Proportional 3D symbols (columns, bars) at point locations, scaled by magnitude. Good for:

City-level aggregations.
Cross-regional comparisons.
Showing individual outliers.

Pros and cons

Pros

Two-variable display in one map.
Visually arresting; increases dwell time.
Intuitive sense of magnitude (tall = lots, short = little).
Builds engagement for non-technical audiences.

Cons

Occlusion — tall features hide what's behind them.
Perspective distortion — farther features look smaller than near ones of equal size.
Reading difficulty — exact values are harder to estimate from 3D bars.
Camera orientation — different rotations produce different impressions.
Print reproducibility — 3D looks good on screen; a single rendered print angle can mislead.

When 3D works

Exploring data interactively (rotate, zoom).
High-impact public communication.
3D makes physical sense (building heights, terrain draped maps).
Paired with 2D views for context.

When 3D fails

Quantitative comparison needing precision.
Print products with a single angle.
Dense urban scenes where occlusion dominates.
Scientific reports (prefer 2D or faceted small multiples).

Terrain-draped maps

A special case: your thematic data drapes over a DEM. Natural for:

Ecology (habitat on terrain).
Geology.
Hydrology.
Tourism.

Use MapLibre's raster-dem source or Cesium with terrain quantized-mesh.

Best practices

Provide interactive controls (rotate, tilt) if your medium supports.
Include a 2D alternative legend (height scale with labeled values).
Use muted colour palettes — saturated colours become overwhelming in 3D.
Add subtle ambient occlusion to help depth perception.
Choose camera angles that minimise occlusion of interesting features.

Self-check exercises

1. A 3D choropleth extruded by population has two counties of similar data values but they look dramatically different. Why?

Perspective — the closer county's 3D bar looks much taller than the farther one even with identical heights. Rotating the camera further elongates or compresses features. For quantitative comparison, 2D is safer; 3D is better for storytelling and exploration. When using 3D, provide the 2D choropleth alongside.

2. Why might MapLibre's fill-extrusion layer be preferable to a static 3D rendered image?

It's interactive — users can rotate, zoom, and tilt to examine hidden data from different angles. Static renders bake in a single perspective that may hide important features. MapLibre's GPU rendering is also smooth and performant on modern browsers, making 3D exploration practical.

3. When would you use a 3D thematic map for scientific communication?

Rarely. Scientific audiences need precise readability; 3D introduces ambiguity. Use 3D when you're visualising genuinely 3D data (urban form, terrain, subsurface geology) or when you need to engage a non-technical audience. For quantitative scientific claims, 2D with rigorous colour ramps and classifications remains the standard.

Summary

3D extruded maps visualise two variables (colour + height) at once.
Occlusion and perspective distortion are real trade-offs.
Great for exploration; less great for precision.
Tools like deck.gl and MapLibre make it easy.