Bivariate Tile Grid Map
A geographic grid of equal-sized tiles where each tile’s color encodes two variables at once — combining the fairness of tile grid maps with the richness of bivariate color schemes.
// 01 — The chart
What it looks like
A bivariate tile grid map showing the relationship between median income and education level across US states. Each tile’s color is determined by where it falls on the two-axis legend.
// 02 — Definition
What is a bivariate tile grid map?
A bivariate tile grid map replaces the irregular shapes of geographic regions with equal-sized tiles (usually squares or hexagons) arranged in a layout that approximates their real-world positions. Each tile is then colored using a two-dimensional color scheme that encodes two data variables simultaneously.
This chart type solves two problems at once. First, it gives every region the same visual weight, preventing large-area regions from dominating the map. Second, it lets you see the relationship between two variables in geographic context — something that would normally require two separate maps.
The bivariate legend (usually a 3×3 or 4×4 color matrix) is the key to reading the map. One variable controls horizontal position in the legend and the other controls vertical position, producing a blend of colors that reveals geographic clusters where both variables are high, both are low, or where one dominates.
Key insight: Bivariate tile grid maps are especially popular in US state-level analysis because the standard geographic map makes small but dense states (e.g., New Jersey, Connecticut) almost invisible while Wyoming and Montana dominate the canvas.
// 03 — Anatomy
Parts of a bivariate tile grid map
// 04 — Usage
When to use it — and when not to
- You want to compare two variables across regions without area distortion
- Regions vary dramatically in geographic size but are equally important
- You need to reveal geographic clusters where two variables co-occur
- Your audience is familiar with the geographic layout being displayed
- You have a small set of regions (e.g., US states, EU countries) that fit a grid
- You want to highlight correlation or divergence between two metrics
- Your audience cannot interpret the bivariate color legend — it requires training
- You have too many regions (>60) for tiles to remain readable
- Precise geographic shapes or boundaries matter for your analysis
- You only have one variable — use a simpler univariate tile grid map instead
- Your two variables are highly correlated, making diagonal colors dominate
- You need to show continuous spatial patterns — use a standard map projection
// 05 — Reading guide
How to read a bivariate tile grid map
Follow these steps whenever you encounter a bivariate tile grid map.
Study the bivariate legend first
The legend is a small color matrix (usually 3×3). Understand which variable maps to each axis. One axis goes left–right, the other goes top–bottom. Corner colors represent extremes.
Learn the corner colors
Identify the four corners of the legend: high–high, high–low, low–high, and low–low. These are your anchor colors. Once you know them, you can interpret any tile’s position in the two-variable space.
Scan the map for color clusters
Look for geographic regions where tiles share similar colors. These clusters tell you where both variables behave similarly — or where one dominates the other.
Look for diagonal vs. off-diagonal colors
Tiles along the legend’s diagonal (low–low to high–high) show correlation. Off-diagonal tiles (high–low or low–high) show divergence between the two variables.
Note outlier tiles
A single tile in a contrasting color surrounded by different colors deserves investigation. It may indicate a region where the two variables have an unusual relationship.
// 06 — Pitfalls
Common mistakes
×Using too many color classes
Fix: Stick to a 3×3 grid. A 5×5 legend produces 25 colors that are virtually impossible to distinguish.
×Choosing perceptually non-uniform color scales
Fix: Use well-tested bivariate palettes (e.g., Joshua Stevens’ schemes). Colors must be distinguishable by hue, not just lightness.
×Omitting the bivariate legend
Fix: The map is unreadable without the legend. Always place it prominently — not hidden in a footnote.
×Placing tiles in wrong geographic positions
Fix: Verify tile placement against a reference grid. Even small errors break the reader’s geographic intuition.
×Ignoring color-vision deficiency
Fix: Avoid red-green bivariate schemes. Test your palette with a CVD simulator to ensure all combinations remain distinguishable.
// 07 — In the wild
Real-world examples
US income vs. education
Newsrooms use bivariate tile grid maps to show how median household income and college graduation rates covary across all 50 states, revealing that high-income states with low education rates (and vice versa) cluster in specific regions.
Health outcomes vs. access
Public health agencies map life expectancy alongside insurance coverage to identify states where outcomes are poor despite good access, or vice versa.
Election analysis
Political analysts use bivariate tile grid maps to show voter turnout alongside margin of victory, revealing whether landslide wins come from high or low participation.
// 08 — Quick reference
Key facts
// 09 — Variations
Types of bivariate tile grid maps
The basic concept has several important variations depending on tile shape and legend design.
Square tile bivariate
The most common form. Square tiles align neatly to a grid, making the layout easy to construct and read.
Hexagonal tile bivariate
Hexagonal tiles create a more organic feel and provide six neighbors per tile instead of four, enabling finer spatial adjacency.
4×4 bivariate legend
A 4×4 grid produces 16 color classes for finer discrimination, but demands more effort from the reader to decode.
Interactive tooltip variant
Interactive versions show exact values on hover, compensating for the difficulty of reading bivariate colors precisely.
// 10 — FAQs
Frequently asked questions
What is a bivariate tile grid map?+
A bivariate tile grid map replaces the irregular shapes of geographic regions with equal-sized tiles (usually squares or hexagons) arranged in a layout that approximates their real-world positions. Each tile is then colored using a two-dimensional color scheme that encodes two data variables simultaneously.
When should you use a bivariate tile grid map?+
Use a bivariate tile grid map when you want to compare two variables across regions without area distortion. It also works well when regions vary dramatically in geographic size but are equally important, and when you need to reveal geographic clusters where two variables co-occur.
When should you avoid a bivariate tile grid map?+
Avoid a bivariate tile grid map when your audience cannot interpret the bivariate color legend — it requires training. It is also a poor fit when you have too many regions (>60) for tiles to remain readable, or when precise geographic shapes or boundaries matter for your analysis.
Is a bivariate tile grid map suitable for dashboards?+
Yes — a bivariate tile grid 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 bivariate tile grid map?+
Bivariate Tile Grid 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 bivariate tile grid 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.