Perceptually Uniform Colormaps.
Use sequential / diverging scales. Never rainbow.
Rainbow colormaps create visual boundaries where none exist in the data because human color perception is non-linear. Use sequential scales (viridis, inferno) for ordered data and diverging scales for data with a meaningful midpoint. Never use rainbow.
Cynthia Brewer, 1994 · ColorBrewer · Adopted by matplotlib, D3, Tableau
Charts that apply this principle
Choropleth Map
Regions colored by value, the most common thematic map type.
Tile Grid Map
Each region is a square tile in a grid with equal visual weight and no geographic distortion.
2D Contour Plot
Contour lines showing density of points in 2D space, like a topographic map.
Correlogram
Symmetric grid of every variable pair's correlation coefficient, with circle size encoding magnitude and color encoding sign — diagonal blocks of strongly-correlated variables jump out instantly.
Heatmap
Color-coded matrix revealing patterns across two categorical dimensions.
Hexbin Plot
Aggregates dense scatter points into hexagonal bins colored by count.
Heat Table
Data table with cells colored by value - spreadsheet meets heatmap.
Isoline / Contour Chart
Lines connecting equal values - like elevation contours on a topographic map.
Calendar Heatmap
Daily values mapped to a calendar grid, revealing day-of-week and seasonal patterns.
Horizon Chart
Layered, folded area chart that shows many time series in minimal vertical space.