How to Show Your Progress With Color Alone

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"Color is a power which directly influences the soul." -Wassily Kandinsky

It’s August, so it seems appropriate to talk about heat maps. I’ve blogged about this simple yet powerful chart type before. It takes advantage of the power of color like no other chart I know. Heat maps use variations in color to show differences among categories (e.g. people living in different zip codes) or differences across a scale (e.g. people with different income levels). In a lot of cases, it’s simply a table with color added to the cells.

The enormous potential of a heat map is clear in Philip Bump’s recent heat map in The Washington Post, which took its inspiration from Thomas Wood’s similar chart. As Bump notes, this chart is “elegantly simple.” The rows are states, grouped by region. The columns are presidential election years. And shades of red and blue indicate the parties of candidates who won in each state, with darker shades indicating wider margins. Here’s part of the chart:

Source: The Washington Post, August 24, 2021

Source: The Washington Post, August 24, 2021

By carefully grouping the states into regions and subregions, the chart reveals interesting patterns: shifts from blue to red (and vice versa) as well as shifts from greater to lesser margins (and vice versa).

Think about how you can show change over time in the problems you are addressing or the services you are offering using color and strategic groupings. Here are some possible applications for organizations like yours:

  • Show shifts in service use over time among two (or more) groups such as adults represented by one color and children represented by another. Each row might be a zip code area and rows could be grouped by city.

  • Show changes in pollution over time produced by two (or more) sources such as vehicles represented by one color and factories by another. Each row might be a country and rows could be grouped by continent.

  • Show variation in client make up over time among two (or more) groups such as higher income groups represented by one color and lower income groups by another. Each row might be a program site and rows could be grouped by neighborhood.

You can create heat maps in many data viz programs. Here is how to create them in Excel and in Tableau.

Let’s talk about YOUR data!

Got the feeling that you and your colleagues would use your data more effectively if you could see it better? Data Viz for Nonprofits (DVN) can help you get the ball rolling with an interactive data dashboard and beautiful charts, maps, and graphs for your next presentation, report, proposal, or webpage. Through a short-term consultation, we can help you to clarify the questions you want to answer and goals you want to track. DVN then visualizes your data to address those questions and track those goals.

Why You Should Know About Heat Maps

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My 2020 gift to you? A quick and dirty introduction to a bunch of different chart types. Over the next several weeks, each 60-second data tip will introduce (or re-introduce) you to a particular chart type. I’ll give you need-to-know information in a format akin to the “Drug Facts” on the back of medication boxes: active ingredients (what the chart is), uses (when to use it), and warnings (what to look out for when creating the chart). I’ll also add some fun facts along the way. The idea is to fill up your toolbox with a variety of tools for making sense of data. We begin with the heat map.

Active Ingredients (What is a heat map?)

A heat map is a chart that uses variations in color to show differences among categories (e.g. people living in different zip codes) or differences across a scale (e.g. people with different income levels). In a lot of cases, it’s simply a table with color added to the cells.

Uses

Consider adding color to a table to quickly see patterns. Tables have a least one advantage over charts. They cram a lot of data onto a single screen or page. But it’s hard to see patterns when looking at a regular table on a spreadsheet. Take a look (but only for a few seconds) at this table showing the number of shelter beds used by individuals and families each month in Chicago.

Are any patterns jumping out at you? Now take a few more seconds to look at this version, which uses color instead of numbers — aka a heat map:

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Are patterns more apparent now? In a few seconds, this is what I saw:

  • More variation by year than by month.

  • Shelter bed usage was particularly high in 2015.

  • Less seasonal variation than I’d expect. I expected darker colors during the winter months.

With a little more time, more patterns might emerge. And more questions too. This heat map shows number, rather than percentage, of beds used. So, perhaps, more beds were used in 2015 because the number of beds available increased. After more examination and exploration, you might decide to use another chart, which zooms in on a subset of the data. But the heat map is a great first step to understanding data.

Warnings

When creating heat maps, you will use discreet colors to show differences among different categories and a color scale (light to dark) to show differences among different levels, from low to high values. Sometimes folks use the stoplight color system (red, yellow, and green) to show the categories: good, okay, and bad. For example, fundraising amounts over a certain number might be considered good. The problem with this approach is that it doesn’t work for people with red-green color-blindness. If you want to draw attention to good or bad amounts, it’s better to just highlight the good or bad numbers with one color and not color the others.

Color provides only a general understanding of differences in data. To provide a more specific understanding you may want to add numbers, as well as color, to cells as in the chart below. And, in general, don’t use too many colors in your heat map palette. It will be easier to read if you keep it simple.

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Fun Fact

Heat maps are thought to have originated in the 19th century. Loua created this chart in 1873 to show the characteristics of 20 districts in Paris.

Let’s talk about YOUR data!

Got the feeling that you and your colleagues would use your data more effectively if you could see it better? Data Viz for Nonprofits (DVN) can help you get the ball rolling with an interactive data dashboard and beautiful charts, maps, and graphs for your next presentation, report, proposal, or webpage. Through a short-term consultation, we can help you to clarify the questions you want to answer and goals you want to track. DVN then visualizes your data to address those questions and track those goals.