Accessibility, Data Visualization, Microsoft Technologies, Power BI

Power BI Report Accessibility Checklist

In many cases, some small changes can go a long way in making your Power BI reports more accessible for users with different abilities. The checklist below lists considerations you should make in your report design to create more inclusive reports. I’ll update this post as new features are released.

Accessibility Checklist

All Visuals

  • Ensure color contrast between title, axis label, and data label text and the background are at least 4.5:1.
  • Avoid using color as the only means of conveying information. Use text or icons to supplement or replace the color.
  • Replace unnecessary jargon or acronyms.
  • Ensure alt text is added to all non-decorative visuals on the page.
  • Check that your report page works for users with color vision deficiency.

Slicers

  • If you have a collection of several slicers on your report pages, ensure your design is consistent across pages. Use the same font, colors, and spatial position as much as possible.

Textbox

  • Ensure color contrast between font and background are at least 4.5:1.

Visual Interactions

  • Is key information only accessible through an interaction? If so, rearrange your visuals so they are pre-filtered to make the important conclusion more obvious.
  • Are you using bookmarks for navigation? Keyboard users can’t select images to go to a hyperlink or bookmark. Try navigating your report with a keyboard to ensure the experience is acceptable for keyboard-only users.

Sort Order

  • Have you purposefully set the sort order of each visual on the page? The accessible Show Data table shows the data in the sort order you have set on the visual.

Tooltips

  • Don’t use tooltips to convey important information. Users with motor issues and users who do not use a mouse will have difficulties accessing them.
  • Do add tooltips to charts as ancillary information. It is included in the accessible Show Data table for each visual.

Video

  • Avoid video that automatically starts when the page is rendered.
  • Ensure your video has captions or provide a transcript.

Audio

  • Avoid audio that automatically starts when the page is rendered.
  • Provide a transcript for any audio.

Shapes

  • Avoid using too many decorative shapes. They are announced by the screen reader when reading the page.
  • When using shapes to call out data points, use alt text to explain what is being called out.

Images

  • When using images to call out data points, use alt text to explain what is being called out.
  • Avoid using too many decorative images. They are announced by the screen reader when reading the page.

Custom Visuals

  • Check the accessible Show Data table for custom visuals. If the information shown is not sufficient, look for another visual.
  • If using the Play Axis custom visual, ensure it does not autoplay. Make it obvious that the user must press the play/pause button to start/stop the changing values.

Power BI Accessibility Features

Tools to Check Accessibility in your Power BI Report

Keyboard Only Navigation

  • Use a keyboard to navigate and interact with your report, without using a mouse.

Color Vision Deficiency

Low Vision

  • Use a mobile device with brightness on low to test mobile reports
  • Use WebAIM or Accessible Colors to check color contrast of text vs background
  • Use The Squint Test to check that a Power BI report makes sense to someone with low vision

If you would like to suggest an update to the list, feel free to leave a comment on this post.

Data Visualization, Microsoft Technologies, Power BI

Choosing a Color Palette For Your Power BI Report

Color is a powerful attribute in data visualization. In a good visualization, it can focus attention and enhance meaning and clarity. When color is used poorly, it creates clutter and confusion. Power BI has a default color palette, but it isn’t always optimal or even appropriate for many reports. Luckily, Power BI allows you to use any color that can be defined by a hex code where visuals allow colors to be changed. With so many choices, choosing a color palette can be overwhelming. Below are some tips to help you choose a good color palette for your Power BI reports.

A color palette is simply a collection of colors applied to the visual elements in your report. What we typically refer to as color is a combination of three main properties: hue (base color on the color wheel), intensity (brightness or gray-ness) and value (lightness or darkness). You can build an engaging and professional looking report with just 6 colors. It’s possible to have fewer colors or more colors, but 6 should cover many common visualization needs. If you are using more than 6 colors, you might want to check that you are optimizing engagement and cognitive load.

  1. Main color – default color on graphs
  2. Color 2 – used when multiple colors are needed in a graph or report
  3. Color 3 – used when multiple colors are needed in a graph or report and Color 2 has already been used
  4. Highlight color – a color used to highlight important data points to make them stand out from other points on the page
  5. Border color – a light color used for borders on tables and KPIs where necessary
  6. Title color – color used for visual titles and axis labels as appropriate

Example Power BI color palette with 6 colors

While your title and border colors don’t have to be variations of gray, gray is a practical color for these purposes when using a white background. You could also use brown, blue, purple, etc. You just want to ensure that your text color has sufficient contrast from its background and that it isn’t more intense than your data colors. I tend to make my border color a tint of the title color.

This is a good place to define a few terms. A hue is a base color without black, white, or gray added, which you might find on a basic color wheel. A shade is achieved by adding black to any pure hue, making it darker. A tint is achieve by adding white to a pure hue, making it lighter. A tone is achieved by adding gray to a pure hue, making it less saturated and more muted.

I think it’s easiest to start your color palette by choosing the main color. This could be inspired by your corporate color palette or logo, your favorite color, or a color associated with the subject matter of your report. Be aware that color has cultural meaning and conveys emotion, and you want to choose a color that conveys the appropriate tone of your report. This can get tricky, so just try to make sure you don’t choose a main color that has a lot of cognitive dissonance with your subject. For instance, if you are creating a report for a U.S. audience about our gun violence problem, you probably wouldn’t use a light, happy, pastel green as your main color. But you could be fine using a bright red, dark blue, orange, black, or several other colors.

You will want to choose a main color that has a medium intensity.  If it is too bright or too dark, you won’t have any room to use a more intense version of that color to focus attention. And since you want your main, secondary, and tertiary color to be the same intensity, it would feel as if everything on the page were yelling at you if all three colors were bold. If you are starting from a corporate color palette, be aware that most brand color palettes were designed for websites and print collateral, not data visualization. They are usually too intense or bright to serve as your main data visualization colors. But you can use a tint or tone of your corporate colors so your reports stay on brand.

Once you have chosen your main color, you need to decide what type of color scheme you would like to use. Common options include:

  • monochromatic – tints and shades of a single hue
  • complementary – colors that are opposite each other on the color wheel
  • analogous – colors that are next to each other on the color wheel
  • split complementary – a base color plus two colors that are adjacent to its complement on the color wheel
  • triadic – colors that are evenly spaced on the color wheel

Example color schemes from ColorHexa.com

My current favorite tool for choosing colors is ColorHexa. It provides hex colors, color schemes (as shown above), tints, shades, and tones.

Once you have made some initial color choices, test it out on a few charts to ensure you can answer yes to the following questions:

  • Are all colors easily distinguishable from each other? If you were to use the main, secondary, and tertiary color in a line chart, could you easily follow the lines as they cross each other?
  • Is your color palette color blind friendly? You can use ColorHexa or Coblis to check this. It’s not always obvious when you have people with color vision deficiency in your intended audience, so it’s better to use colors that are easily distinguishable by those with red-green color blindness (deuteranomaly, deuteranopia, protanomaly, and protanopia).
  • Does your highlight color have high contrast from your other colors so it is obvious that it is being used to draw attention to a trend or data point?
  • If you are using a non-white background color, do your colors stand out sufficiently from your background?
  • When you look at your color choices, do you find the combination generally appealing, balanced, and not overly jarring? This is a bit subjective, but if you look at your colors and have a negative reaction then your audience will probably have a similar reaction.

Finally, be aware that colors display differently on different screens and surfaces. You can put a lot of time and effort into choosing the perfect colors, then share a report with someone and have it look rather different on their monitor or when viewed on a projector screen. If you can, review your colors on the equipment that your intended audience will most commonly use to make sure it looks good for them.

If you are still having trouble choosing colors, you can check out the Power BI Report Theme Gallery for some inspiration. Not every example in the gallery shows good color choices, but you can still use it to get ideas.

Once you have your color palette, you can reuse it in future reports by making a report theme. And if you aren’t a fan of manually writing JSON for your report theme, check out the Report Theme Generator from PowerBI.Tips. If you define your colors in a report theme, Power BI will create tints and shades of your colors for you, saving you the trouble of having to look them up yourself.

Power BI Color Picker

If you have advice to help others choose colors, leave a comment on this post or tweet me.

Accessibility, Data Visualization, Microsoft Technologies, Power BI

Power BI Screen Reader Accessibility

I recently wrote a post on the BlueGranite blog called Improving Screen Reader Accessibility in Power BI Reports. It contains some good reasons why accessibility should be considered when it comes to usability features of any web property or data viz. And it shares several tips to make your report more accessible to screen readers and those who navigate via keyboard only. This all came about because I got the chance to work with my friend Dave Bahr, an accessibility specialist who is also blind and an advanced user of screen readers. He helped me test various features and do the screen capture you see in the video embedded in the BlueGranite blog post.  It was a very interesting and enlightening experience that provided enough content for multiple blog posts. So here’s my second blog post (the first on my Data Savvy blog) with more of what I learned from this experience.

Power BI is off to a good start with screen reader accessibility and keyboard navigation, but there are some gaps. They have added keyboard shortcuts to navigate between pages, examine the visuals on a page, and show the data in an accessible format. These features are consistent across Power BI Desktop and PowerBI.com. Keyboard shortcuts for Power BI reports

It’s also pretty cool that when the screen reader encounters a visual on the report page it announces the visual title, the chart type, and the alt text. Why does this matter? When we talk about charts on a report we tend to say something like “That sales by region bar chart is…[interesting/not showing correct data/etc.].” Now someone using a screen reader can also follow that reference. Props to the Power BI team for making that work. Based upon my testing so far, it also works on custom visuals (for the most part).

Keyboard (and screen reader) users can also access the menu options to drill down a level and expand down a level. When they do this, the accessible Show Data table changes to what is currently shown in the visual.

Power BI Show Data table at top level
Show Data table at top level
Power BI Show Data table after expanding down a level
Show Data table after expanding down a level

The data in the accessible Show Data table will render in the order it is shown in the visual, so you can control that in your design. One exception to this is when the data is rendered in a matrix rather than a table: the total in the accessible Show Data table is positioned at the top rather than the bottom where we see it visually. This is a purposeful design decision to help the user understand the total and then the breakdown of subtotals. Another good thing about the accessible Show Data tables is that tooltips are included, just like when we use the See Data feature.

Another nice feature (not sure if this is built in to JAWS or something the Power BI team added) is that if you have a report page that takes a while to load JAWS will say “Alert: Visual are loading” so it’s obvious to a blind/low vision user that they need to wait to get the full report page.

There is still a bit of work to be done to make Power BI truly accessible to screen readers. Currently, keyboard users cannot interact with visuals on the page. This means that users who do not use a mouse cannot:

  • Click a bar in a bar chart and see other charts on the page cross-filter/cross-highlight
  • Drill down on a single value within a chart
  • Select a value in a slicer
  • Click on a hyperlink in a table or text box
  • Click on an image that is linked to a bookmark or external hyperlink
  • Play or stop audio or video that requires user interaction

This seems like a tall order from a development standpoint. But there are other features that require less effort that could make a big difference in the user experience of a screen reader/keyboard user. I have logged ideas for each of these features, and I hope you will add your vote to my ideas.

  1. Currently, a keyboard user presses the Tab key to move between visuals on a page.  The order in which they arrive at visuals is arbitrary. In Power BI Desktop, it seems to be the order in which the report designer placed the visual on the page. The behavior in PowerBI.com was the same until this month. Now I’m not sure what the order is there.  Most of us design reports that guide our users through a path, with information placed in a specific order that follows their line of thinking/questioning. Keyboard users can’t easily follow the visual order we have imposed because the tab order is basically random (from their point of view). I thought I had a workaround by creating a new report page and copying the visuals over to the new report page in the desired navigation order, but that now only works in Power BI Desktop and not the web service. It would be fairly easy to expose a property in the formatting pane that allows the report designer to set the tab order. Then they could tab in the order we want a user to consume the content. In the image below, the yellow numbers are the current tab order created by Power BI and the green numbers are desired tab order.  I would like the user to consume the left side of the report from top to bottom and then consume the right side of the report from top to bottom. But currently, screen reader users get sent all over the page in an unhelpful order. Please vote here for adding Expose tab order as a property of visuals for keyboard navigation.
  2. When we add hyperlinks in tables, users can click on them to navigate to the target of the link. Users who navigate via keyboard currently cannot do this. There is no way to click on the link. The URL does show up in the accessible Show Data table, but the user has to use the keyboard to find the URL, select it, copy it, and then open a web browser and paste the URL into the address bar. It should be possible to render the URL as a link rather than just text, so a user with a screen reader could just select the link and use it to navigate to the target destination. Please vote here for Make columns containing urls have embedded hyperlink in accessible show data table.
  3. While there is an option to add alt text to each visual, that text is static. So there is no way to use alt text to provide a summary of trends in the chart without manually updating the alt text each time the data is updated. It would be great if the alt text could be populated by fields in the data model. Just like we now have a Tooltips section, we could have an Alt Text section to drag fields into. Where fields in tooltips apply to a specific data point, fields in alt text would be an aggregation over the total data used in the visual, e.g., in a chart that shows sales by month, the alt text would show total sales or last sales amount (depending on what measure was dragged in). But that would be a great start.
    Mockup of requested Alt Text section in the Fields Pane of Power BI
    Mockup of requested Alt Text section in the Fields Pane of Power BI

    The ideal feature for this would be to do something like the Englighten Data Story custom visual where you can add text and then placeholders for fields, then add the fields in the order you want them to fill the placeholders. That would be a bit more complicated, so I would gladly settle for just being able to drag fields into an Alt Text section and have it show summary numbers.  Please vote here for Allow use of field value to populate alt text.

  4. Make textboxes accessible to screen readers. Currently, the contents of a textbox can’t be read via screen reader so you must resort to copying the content to the alt text property. When a user uses the Show Data keyboard command, nothing is available for the textbox – it’s just blank. At the least, the contents of the textbox should be available in a single column/single row table via the Show Data command. Even better would be to auto-populate the alt text with the textbox contents by default. Even better than that would be to reserve the alt text for other comments and add a different property that would allow a screen reader to read out the contents of that property right after the alt text. Please vote here for Make textbox contents accessible to screen readers.

Some other interesting things I learned:

  • Many blind users have their browsers settings such that they don’t load images. It saves time in loading the page without detracting from their user experience. When browsing a Power BI report with the browser set to not load images, the screen reader still knows an image is there and announces it (“image”), even if it doesn’t appear on the screen.
  • If you use the Play Axis custom visual and allow it to interact with a another visual and then look at the accessible Show Data table for the other visual, the contents will continue to change based upon the changing of values in the Play Axis. While this is rather amusing, I’m sure it makes it difficult for screen reader users to figure out what’s going on and actually obtain information.

Power BI has an opportunity to be a leader in accessibility (of all areas, not just for screen readers). In our increasingly data-driven work cultures, people of all abilities need data. Please help the Power BI team know that accessibility should get some of their limited attention and resources by voting for my ideas or logging your own. If you log an accessibility related idea, feel free to link to it in the comments of this post or tag me on Twitter and I’ll help publicize it.

 

Data Visualization, Microsoft Technologies, Power BI

Design Concepts For Better Power BI Reports Part 5: Affordances

Affordances are a general design concept that comes from physical product design but can be applied to visual design. I first learned about affordances from the book The Design of Everyday Things. The book describes affordances as the following.

“Affordances provide strong clues as to the operations of things… When affordances are taken advantage of, the user knows what to do just by looking: no picture, label, or instruction is required. Complex things may require explanation, but simple things should not.”

Affordances allow us to take advantage of common experiences and cultural standards to create immediate understanding of our designs. Examples of affordances in physical products include:

  • A coffee cup with a handle suggests that you should grip the cup by the handle.
  • Buttons on doorbells are for pushing.
  • The material and shape of balls suggest they are for throwing and bouncing.

In digital design, users form and develop notions of what they can do according to conventions, constraints, and visual, auditory, and haptic feedback. Examples of perceived affordances in web design include:

  • Scroll bars
  • A colored button, such as the Tweet button on Twitter.com
  • A light gray button with light text that indicates the button is not clickable
  • A disk icon used to indicate the save command
  • Breadcrumb navigation

There is also a complementary concept called a false affordance. False affordances give a clue as to usage that does not match the resulting action. There are examples of this all over the web: buttons that do nothing, text that says “click here” but isn’t a hyperlink, a logo that doesn’t return the user to the home page.

Here’s a 5-minute video from Vox Media about bad doors and false affordances. You might remember it from when it made its way across the internet a year or two ago.

Affordances in Data Visualization Design

Affordances are very relevant in data visualization design. I first saw this application discussed by Storytelling With Data. She describes the use of affordances in data viz design as follows:

“Through strategic use of things like color, size of elements, spacial position, and text, it is so clear to the audience how to interact with the data visualization that they don’t even notice the design.”

But she isn’t the only one talking about it.  The idea here is the same: Use existing knowledge and consistent design to make it obvious how users should interact with your data visualization.

Affordances in Power BI

Since Power BI is largely an off-the-shelf product rather than a custom application (with the exception of Power BI Developer features), much of the user interaction is handled by Power BI desktop or the Power BI web service. For instance, Power BI provides the button for Focus Mode and a contextual menu at the top right of each visual on a report page. Tables automatically have interactive sorting, activated by clicking the column header. Hover text exists when you hover over a data point on a chart.

That doesn’t mean we don’t need to pay attention to affordances. The biggest thing we can do as report designers is implement consistent design.

Use a consistent color palette. If users get used to a certain shade of yellow or orange that indicates something needs attention, they will take that visual cue when they see it elsewhere in the report or in the next report. Colors have meaning for us, so we can define colors to indicate good/bad results, or associate colors with categorical values. Power BI Report Themes can be very helpful in this regard, since they can define a color palette and visual formatting.

Using consist placement and formatting of slicers across report pages and reports can also be helpful. If you use the same slicers on multiple reports/report pages, can you use consistent formatting and spacial position?  Do you have a slicer section of your report page where all slicers sit, along the top or left? Could you format your region slicer in a similar manner on every page (e.g., vertically with simple dark text and no background color)? Power BI Report Templates can come in handy in this regard. You can create a template that has the title, slicers, and chart positions and formatting already set.

As fun and interesting as it may be to use a new and shiny custom visual, if that visual doesn’t make its interaction and information obvious to users, it may not be the appropriate choice. There is a reason people like bar charts – they follow common convention and are easy to read.

Another thing to consider is the use of images to link to bookmarks and websites. Make sure it is obvious that your image is clickable, and make sure it’s obvious where clicking that image will take you. If it’s not clear, add some text to indicate that there is a possible interaction there.

Also, be aware of how you use visual interactions. If you choose to edit the default, do so with reason and try to make it obvious through design cues what the expected interaction will be. Otherwise, users might click a slicer or a bar in a bar chart and wonder why values in another chart aren’t being filtered or highlighted.

This is not to say you should never try anything new or deviate from the norm, but that you should do so purposefully when learning a new design/convention is worth the effort to your users. The consistency and simplicity of affordances corresponds to reducing extraneous cognitive load.

Finally, be aware that affordances are cultural, and may be different across different user groups. For example, colors have different meanings in difference cultures. Be sure you are designing for your intended audience rather than yourself. It can be helpful to confirm with a potential user during user acceptance testing that the design affordance you think is obvious is indeed obvious to them.

 

This post is part of a series. Go here to see the list of posts in the series. 

Data Visualization, Microsoft Technologies, Power BI

Design Concepts For Better Power BI Reports Part 4: The Squint Test

Data visualization should be iterative. You should get a good initial draft put together and then check to make sure it meets your success criteria. Then check the design to ensure it it effectively conveys information in a manner that is easy for your audience to consume. You can then make some changes and check things again. One design check you’ll want to perform is the Squint Test.

The Squint Test helps you check the effectiveness of the layout and design of the elements in your report. You can perform the Squint Test using one of two methods:

  1.  Lean/step back from your screen and partially close your eyes.
  2. Use an application that blurs the details of a web page containing your report or an image of your report, creating an effect similar to squinting.

This allows your design to become blurry, removing visual detail so only the largest, most rudimentary shapes are seen.

When you squint at your report/dashboard, you’ll notice the overall layout and the elements that stand out most. In other words, the Squint Test gives you a high-level view of the visual hierarchy of your work. This is a great way to check that you are making good use of preattentive attributes and Gestalt principles!

Here are some questions to ask yourself while performing the squint test:

  • Are any foreground elements not standing out enough against their background?
  • Are there any background or border elements that unintentionally draw more attention than more important data elements?
  • Is the most eye-catching element on your report page an important element?
  • Are your charts in an appropriate order on the report page?
  • Are elements spaced appropriately so that objects that are closer to each other have some type of relationship?
  • Is the report page balanced so one side is not heavier than another? Is the amount of white space on each side of the report fairly even?
  • Are there colors that “pop” more than other colors? Are the items that pop intentionally highlighted or accidentally overly prominent?

Performing the Squint Test in Power BI

While you can definitely perform the Squint Test on your report within Power BI Desktop, I recommend also testing in a browser once the report is deployed to PowerBI.com or to the Power BI Report Server portal since colors and objects may be slightly different there.

The Squint Test is also used in web page design, so web developers have made tools to aid them in this check. While just squinting at the page is perfectly sufficient, using a browser extension or another tool allows you to easily share your findings with others. In the Chrome Browser, there is a free extension called The Squint Test. This extension places an eye icon near the top right of the browser window. Clicking the icon provides a slider that allows you to increase or decrease the amount of blur applied to the page.

The Squint Test Browser Extension
The Squint Test Browser Extension

I usually turn the blur to about 6 to perform my Squint Test.

As an example, below is a draft of a report page I made earlier this year. The first image is the original report, and the second image is the blurred version to be used for my test.

BloodGlucoseReportClear BloodGlucoseReportBlur

My thoughts from my squint test:

  • I don’t use a lot of chart backgrounds, and my report page background is a very light gray. So they aren’t overshadowing any objects in the foreground.
  • I also don’t use chart borders, so things look good there.
  • The items that stand out the most are the image in the top left with the glucometer and tomatoes, the matrix with conditional formatting that shades the cells blue, and the box and whisker plot in the lower left quadrant. I’m ok with these items being the most prominent. Although the image could be considered decorative, the image is helpful in explaining the information contained in the report (glucose readings).This is more meaningful when viewing the full report with multiple report pages. The other two prominent elements are displays of data. The matrix is most prominent where readings are high and needing attention. The box and whisker plot is a good summary of glucose levels throughout the day.
  • Charts seem to be in a logical order. Flowing left to right, I get some quick summary numbers and trends, individuals readings that explain those trends, the readings shown based upon time of day, the range of readings throughout the day, and then a longer term view of readings throughout the day over time.
  • When I look at spacing, I think the matrix needs to be moved to the right to make the space between it and neighboring graphs more even. The matrix is not more related to the sparklines and KPIs to the left than it is to the line chart to the right.
  • One could argue that the page is a bit unbalanced, since the scatter plot and the line chart are a bit less prominent than the other graphs on the left side of the page. I think moving the matrix to the right a bit plus the use of the dark purple colors, evens it out somewhat.

After reviewing my findings, I could make the necessary changes and then check it again, iterating until I am satisfied.

Now you can use the Squint Test to check your visual hierarchy of information and improve the efficacy of your Power BI reports. Happy squinting!

This post is part of a series. Go here to see the list of posts in the series. 

Data Visualization, Microsoft Technologies, Power BI

Design Concepts for Better Power BI Reports Part 3: Gestalt Principles

The Gestalt principles of visual perception describe how humans tend to organize visual elements into groups or unified wholes to help us make sense of visual stimuli. Basically, we perceive the visual world as complete objects rather than a bunch of independent elements.

For instance, you probably see a triangle in the white space in the first image below. And in the second image, you probably see a rectangle.

Your brain is simplifying visual elements into what it commonly finds them to be (the triangle and rectangle).

There are 8 Gestalt principles that are particularly relevant to data visualization:

  • Proximity: We perceive objects that are close to each other as being in the same group
  • Similarity: We perceive visually similar (by color, shape, etc.) as being in the same group.
  • Closure: We perceive objects as being whole even when they are not complete (such as the rectangle above).
  • Symmetry: We tend to perceive objects as being symmetrical and pivoting around a center point.
  • Common Fate: Objects are perceived as lines that move along the smoothest path
  • Continuity: We perceive objects that are aligned with each other as being in a single group or object, creating a single path or shape rather than multiple distinct paths or shapes.
  • Good Gestalt/Prägnanz: We like to find simple patterns. We perceive objects as related if they form a pattern that is regular, simple, and orderly.
  • Past Experience: We categorize visual stimuli based upon our past experience. If objects are usually perceived close together in time or space, we tend to see them as being related. This is how we recognize letters and words.

Here’s a 20-second video I found that illustrates many of these principles.

None of the Gestalt principles work in isolation – you’ll usually find multiple principles at work simultaneously.

Gestalt Principles in Power BI

Gestalt principles can help us highlight patterns and reduce noise in data visualization. They can also help us create a visual hierarchy and employ symmetry in our designs for a more pleasing user experience.

Some Gestalt principles are very similar to our understanding of preattentive attributes. This is demonstrated in the set of 3 charts below.

GestaltContinuity1
This chart is not following the Gestalt Principle of Continuity
GestaltContinuity2
Chart rearranged to better follow the Gestalt Principle of Continuity
GestaltContinuity3
Chart rearranged to follow the Gestalt Principles of Continuity and Similarity

In the top chart, bars are ordered alphabetically by product name. In the middle chart, we changed the bar order to be descending by sales amount. This satisfies our need for the trend to make a smooth descending path as seen in the Gestalt Principle of Continuity. In the third chart, we have changed the color of the bars to all be the same. The color of the bars didn’t have any special meaning, and the entire chart used the same categorical axis and measure. This follows the Gestalt Principle of Similarity. Instead of seeing individual bars, we now see them more as a group of bars.

Here’s another example.

GestaltProximity

In the top chart, try comparing sales for each product within a quarter. Which product had the highest sales in Q3? This should be fairly easy. Now try using the top chart to compare the sales for Product B over time. It’s a bit more difficult because you have to pick out the blue bar in each cluster.

Now try using the bottom graph to examine sales for Product B over time. It should be much easier because the bars for each quarter are close together.

You can see these charts on PowerBI.com here.

What Does This Mean For Report Design?

Here are some things you can do to take advantage of Gestalt Principles in your Power BI reports:

  1. Check your placement of charts on the report page. Are charts that are closer to one another actually more related than other charts that are not as close together? Are you leaving enough white space between visuals so that we can tell where one visual ends and the next begins?
  2. Be sure to group things appropriately for the most common analysis to be performed, such as with the clustered bar chart example above. Proximity of objects within a graph is important.
  3. In simple bar charts with one category and one measure, use only one color on the bars, unless you are purposefully trying to highlight a trend, grouping, or data point.
  4. Make sure your colors have consistent meaning. If you are using light blue to show sales in one chart, try not to use that same light blue to show expenses in another chart on the same page, unless all your charts on the page or in that section use that color for a specific reason. (Note: It’s possible to make a nice Power BI report with only two colors. I’m not suggesting you use multiple colors all the time. But if it makes sense to use multiple colors, make sure your colors have consistent meanings because those colors imply grouping.)
  5. Order bars/columns by descending or ascending value when not trying to show trend over time.
  6. Use low saturation or neutral hue colors as backgrounds in charts so data points stand out more than the background.
  7. Be careful with network graphs. In these graphs, proximity does not necessarily indicate similarity, and spatial position does not always have a meaning. It’s just an algorithm determining where to place objects within the chart. Check for any false conclusions that may be drawn by these properties and change your chart or add explanatory text to help users understand what information you are trying to convey.

More Information

You can find more information about Gestalt Principles at the following links:

 

This post is part of a series. Go here to see the list of posts in the series. 

Data Visualization, Microsoft Technologies, Power BI

Design Concepts For Better Power BI Reports – Part 2: Preattentive Attributes

Preattentive attributes are visual properties that we notice without using conscious effort to do so. Preattentive processes take place within 200ms after exposure to a visual stimulus, and do not require sequential search. They are a very powerful tool in your data visualization tool box – they determine what your audience notices first when they look at your Power BI report.

Four preattentive visual properties have been defined:

  • Color (intensity, hue)
  • Form (orientation, line length, line width, size, shape, curvature, enclosure, added marks)
  • Spatial Positioning (2-D position)
  • Movement

Below is a short video I found that demonstrates preattentive attributes.

 

 

Preattentive Attributes in Power BI

Every chart you build in Power BI uses preattentive attributes, but you must make design choices to use them purposefully. Here are some quick examples.

Preattentive Color Length 1
Preattentive Attributes: Color and Length
Preattentive Color Length 2
Preattentive Attributes: Color and Length

The chart on the top uses a different color for each bar and orders the bars alphabetically by product. The chart on the bottom uses a single color across all bars and orders the bars descending by sales amount. Notice how your eyes jump back and forth between the colors in the chart on the top. When you look at the bottom chart, your eyes more easily follow the length of the bars down and across the categories from largest to smallest.

Here’s another example.

Preattentive Orientation Enclosure 1
Preattentive Attributes: Enclosure and Orientation
Preattentive Orientation Enclosure 2
Preattentive Attributes: Enclosure and Orientation
Preattentive Orientation Enclosure 3
Preattentive Attributes: Enclosure and Orientation

The vertical bar chart on the top has a dark black border. It’s probably the first thing you notice about the chart.

Once we remove the border, as shown in the chart in the middle, we notice that the chart category labels have a diagonal orientation. They stand out because nothing else in the chart is diagonal. It’s a bit distracting and difficult to read.

The horizontal bar chart shows the same information in the same order, but allows the category labels to remain horizontal. Now our eyes focus on the information encoded by the bars.

Click here to see these examples in Power BI.

What Does This Mean For Report Design?

We need to take advantage of the way we process information to create a faster and more natural way of acquiring information through our Power BI reports. Specifically, we can use preattentive attributes to highlight the most important parts of a visual and to create a visual hierarchy of information. Color is probably the most powerful preattentive attribute we have at our disposal, so we should use it strategically.

Here are some things you can do to take advantage of preattentive attributes in your Power BI reports:

  1. Reserve the use of bright colors for items that need attention from your users or those that should be examined first, and use less intense colors for other items on the page.
  2. Don’t use multiple colors for the sake of having several colors. For instance, a bar chart with only one field on the categorical axis generally doesn’t need to have separate colors for each bar.
  3. Don’t settle for rotated axis labels when they won’t fit horizontally. Abbreviate categories and numbers, or switch to a different chart type that supports longer labels if you need to do so.
  4. Start bar charts at 0 to allow your users to accurately evaluate length and differences between bars.
  5. Make sure visuals in a row are exactly aligned. If charts in a row are slightly misaligned by a few pixels, it can be distracting.
  6. Don’t let chart title be the brightest/boldest thing on your page. Let your data in your charts, KPIs, and cards draw the most attention. In many cases, you don’t need a background color on your chart titles.
  7. Avoid adding dark, intense chart borders. Try using whitespace to separate charts rather than adding borders.

There are times when chart borders and background colors on chart titles are appropriate. (I’m currently working on a report where I have a border around a group of charts to indicate that they are all related, but it is light gray rather than black.) But they definitely aren’t appropriate all the time, so I suggest your default be to avoid them and add them when necessary.

Sometimes it’s difficult in Power BI to find a chart that will accommodate even slightly long category labels, since the built-in visuals truncate the values on the axis with no setting to change that behavior. I ask that you lend your votes and comments to User Voice to help change that. You can vote here or here. Until that issue is resolved, you might try the Attribute Slicer custom visual. Although it has some formatting quirks of its own, it has a setting to define the portion of the chart that should be taken up by the bars versus the labels.

I have provided several guidelines that are not hard and fast rules. The goal of these guidelines is to help you use color, form, and position to guide your users through your report in an efficient manner, to help them process the information your report provides.

 

This post is part of a series. Go here to see the list of posts in the series.