Map Color Choices
Last updated
Last updated
When we provide two datasets with the same name but different years (such as EJSCREEN 2019 and EJSCREEN 2021) then the default columns should be the same between the layers and the color ramps should be the same.
When we provide two datasets that are related to each other, such as Census Community Resilience Estimates and Census Community Resilience Estimates - Equity Supplement, then the default columns should be the same between layers.
Numeric columns should use color ramps that indicate the difference in values across the range of the data. There are two common color ramp types to consider:
Sequential ramps are applied to ordered numerical data, such as floor area ratio or population density. These ramps fade from a dark shade of a chosen color to a very light or white tint of the same hue. The changes in lightness correspond to the data’s progression: lighter hues typically correspond to lower values and darker hues to higher values.
Sequential schemes can use a single hue, like the red one we see at the left, or be derived from multiple hues. This multi-hue example on the right goes from light yellow to dark blue, with green appearing for values in the middle of the progression.
Multi-hue classes are better when you want to be able to distinguish values easily across the entire range of the data distribution. The difference between high and low values is double encoded visually, using both change in lightness and change in hue.
Diverging ramps use a combination of two sequential schemes that diverge from a shared light color that represents a critical break point in the middle.
For example, you could use a diverging ramp to show deviation from an average midpoint, with values on the left showing below average and on the right showing above average. The darker the hue, the further from the midpoint the value is.
Discrete numeric bins are applied to data that is categorical and has distinct boundaries, such as land use, zoning districts, or congressional boundaries. The colors for discrete numeric bins should sample across the color spectrum and be easily distinguishable from one another, as they are meant to convey distinct areas.
Continuous ramps are applied to data that is based on a relative measurement that does not have distinct boundaries, such as walk access, energy usage, or elevation level. The colors for continuous ramps should change in lightness and be based on only one or two hues, as they reflect the progression of numeric values across the data.
To better serve those with red-green colorblindness, try avoiding color ramps with both red and green. Choosing a color ramp that changes from light to dark, in addition to changing hues, can also make the distinction across the ramp values stronger.
Color contrast is defined accordingly:
According to the WCAG Level AA requirement, 4.5:1 is the minimum acceptable ratio.
Depictions of vegetation should typically use shades of green.
Depictions of water should typically use shades of blue.
Depictions of fire hazard should typically use shades of red.
To verify whether the contrast between colors is sufficient, use a free color checker such as the one here: .
In, contrast is a measure of the difference in perceived "luminance" or brightness between two colors.
