ProPublica Data Style Guide
by Scott Klein, ProPublica
This style guide comprises the typographic and technical best practices used by ProPublica's News Applications desk. Many rules here apply to our stories as well as our online graphics and news applications. It's not meant to be a design spec or a coding style guide, though you should probably have both of those.
Using rules consistently can make your job easier and can prevent readers from having to struggle with new interfaces on every project, but remember that overdependence on rules can hamper progress, and that "a foolish consistency is the hobgoblin of little minds." News apps are a new and dynamic field and forking these rules for your own newsroom is a good thing. These rules are not an excuse to avoid change, and nothing in this document should be taken as a discouragement to be weird. This is just a set of decisions we've decided work really well for us, and that we try to stick to.
Finally, this is a living document. Please feel free to propose changes.
The most important thing by far is to be accurate.
A full discussion on how to be sure you're accurate is beyond the scope of this document. Read "Bulletproofing your data-based stories." Now.
Asterisks and footnotes are artifacts of print, and lead to confusion on screen. Use hovers instead.
Always label axes except where the label would simply duplicate the headline or top matter.
Support the current and prior major release of Chrome, Firefox, Internet Explorer and Safari on a rolling basis. If earlier releases represent more than 2.5% of our audience, continue to support them. This varies only slightly from Google's Policy.
If you must use a library or technology that has no cross-browser equivalent, provide graceful fallback on other supported browsers.
Support the built-in browsers in the latest revision of the iOS and Android software development kits. All hover and click events should have analogous touch and swipe events on touchscreens.
When feasible, use responsive web design, with breaks for desktop, tablet and handset. However, if an app or graphic requires so much horizontal space that responsive design would be impractical, make sure that handsets and tablets can see and use those apps in "overview mode."
Bylines are important measures of credit and responsibility. Just as every story has a byline, every news app and graphic should have a byline.
The byline on a news apps or graphic follows the same style as stories. It should never be omitted, and should not appear on the bottom of the page or only on a hidden "credits" screen. In a multi-page app, the byline should be at the top of the first page, under the headline.
The byline should list the developers and reporters who made significant contributions to the app. Be generous with bylines.
Use a bar chart to show discrete quantities.
Use a stacked bar chart to show the relative values of categories and subcategories of data.
Use a line chart (sometimes called a fever chart) to show continuous variables such as time series.
Use a scatterplot to show a correlation (or lack thereof) between two variables.
Bubble charts are acceptable where the accurate perception of fine differences between the circles is not important (see Maps). Circles in bubble charts should vary in area and not diameter or radius.
Avoid 3-D charts at all costs. Humans have enough problem perceiving area accurately. Asking them to perceive 3-D volume makes matters worse.
Avoid donut charts at all costs.
Don't show interpolated or predicted data without saying you're doing so.
In annual trend data don't include partial years.
See also: treemaps
When you select colors, check to be sure people with color blindness can read and understand the data. We use Color Oracle to do this.
Use Color Brewer to select colors when possible, and not just for maps.
When showing differences in rate of a single variable, stick to a single hue and vary value/lightness. For example, don't fade from blue to pink. The one exception is fading from red to green to show "bad" to "good" (and remember to check your reds and greens for color blindness accessibility).
When showing variations in kind, alter hues.
Pick color breaks carefully. Your data may not be best represented with equal-interval breaks. See what patterns emerge using a variety of algorithms, such as quantiles, Jenks natural breaks, head/tail breaks, standard deviation, or even arbitrary breaks that might make sense for your data. For example, if your data is average commute time to work, breaks of 10, 20, 30, 45 and 60+ minutes might make the most sense for readers, even if your data is not distributed normally among those breaks.
Make sure your color breaks don't mislead readers about the distribution of your data. For instance, if your values are mostly clustered between 1 and 10 but includes a few items above 1,000, make sure that the color that represents 1,000 is more than just one shade different than the color that represents 10. The Daily Beast used a tool they made called Histagram.me to examine the distribution of datasets.
If the pattern you see in your data only appears under a custom color break scale, rethink whether the pattern is actually in the data.
News apps and graphics should follow your newsroom's standard corrections policy. Observe the following additions:
When data is incorrect, place the correction language on every page that once showed the incorrect data point. That may mean that a correction will appear on thousands of pages.
When an app's data is refreshed and the corrected data has been removed or superceded, remove the correction language to avoid confusion.
When they're used in a sentence, put spaces around en-dashes and em-dashes, and around double-hyphens when used in place of them. Browsers are really bad at typesetting lines properly when they contain words joined by a dash.
Follow your existing house style on when to use en-dashes and em-dashes. If you don't have a style yet, it's probably safe just to use hyphens everywhere. If the idea of using hyphens instead of the proper dashes horrifies you, by all means do what your heart commands, though remember that you'll be working with data from sources that don't share your strong feelings, so maintaining your style consistently will take some doing.
Data: Singular or Plural?
Singular. Say "this data is" and not "these data are," just as you say "this bacon is delicious" not "these bacon are delicious."
This rule is not without controversy. The AP classifies data as a collective noun that takes the singular when treated as a unit but the plural when referring to individual items ("The data is sound," but "The data have been carefully collected.").
Try to avoid using html entities. We're in the future -- use unicode.
When making maps of geocoded addresses, use the Google Geocoding API and only show addresses that have accuracies of "ROOFTOP" or "RANGE_INTERPOLATED" in the location_type field. Don't display partial matches.
Do spot checks to make sure everything geocoded, and as with all things, bulletproof your data.
(see Top Matter)
The main page of every news app should have a headline.
It's ok to require readers to hover their mouse over an element to see further detail. However, don't use hovers when seeing more than one of them at the same time is needed to understand the app or graphic.
When requiring hovers in blocks of text (as opposed to in a map or graphic), provide a symbol that lets readers know that the hover is available.
It's good to write sentences that include interpolated variables, but the fact that you've done so isn't particularly interesting to the general public. Don't change typographic style to highlight interpolated variables.
(see Top Matter)
It's preferable to label items in a chart directly, but in cases in which that's not possible you should always use a legend that is visible on the reader's computer screen when the chart is visible. Legends should be in the same sequence as the charts they describe.
Maps are best when showing data in which geography is an important variable. Read "When Maps Shouldn't Be Maps" before making any maps.
All maps must be distinguishable from population maps. To accomplish this, the underlying data should control for population or other denominator. If you make a U.S. state choropleth map and the darkest states are New York, Texas and California, re-read this paragraph.
Use the Texas-Centric Albers Equal Area projection (EPSG:3083) for a map of the continental U.S. and state-plane maps for individual states. Use the Mercator projection only for tile maps (sometimes called slippy maps).
Avoid bubble maps, which represent the rate of a phenomenon at different locations using differently sized circles. This is for two reasons: First, people cannot accurately perceive differences in the area of circles. Second, bubble maps appear to show the geographic bounds of a phenomenon and not the rate of that phenomenon at the geographic center of the circle. This is another way of saying that they look too much like nuclear blast radius maps.
Every page in an app should have a unique title tag, a unique meta-description tag and the correct social media tags specific to that page.
News Applications vs. Graphics
News applications and graphics share a lot of characteristics. Both tell stories with data. Both are an amalgam of design, programming and journalism. So what's the difference? Here are two criteria. One is more technical and so less open to debate, but we admit they're both imperfect:
- Graphics tend to tell a single story while news applications tell many -- specifically, news applications let readers see how they're personally affected.
- Graphics tend to run in the browser while news applications tend to require multiple trips to some backend or a runtime on a server.
Document any methodology and present it to readers clearly. Post a link to it prominently in the app or graphic. The methodology (or "nerd box") should detail the sources of the data, the steps you took to clean the data and the exact analysis you ran on the data.
Use the appropriate currency symbols when showing currency. Avoid showing fractional currency like cents. In most cases, currency for multiple years should be adjusted to current year.
If you are comparing currency (such as costs, revenues, etc.) across multiple years, you should adjust for inflation. Don't ever refer to an amount of money being a "record" based on historical data that is not adjusted for inflation.
Always explain to readers whether and how you've adjusted currency figures.
The primary function of numbers in a news application or graphic is to help readers understand scale and order of magnitude, and compare against other numbers. Think of them more like words than like minutely precise coordinates (unless of course your numbers are literally coordinates).
Apply the following rules to numbers wherever they appear in your apps and graphics:
Except where special precision is required, stick to whole numbers. Don't portray precision that doesn't really exist.
When displaying numbers in a table, make them either right-aligned or decimal-aligned.
Round numbers and never use 'ceiling' or 'floor' functions for floats. Be vigilant if your programming language does this by default.
Except where special precision is required, abbreviate any number over 10,000 by truncating each number after the highest thousands place and appending a word or abbreviation indicating order of magnitude. Use one significant digit after the decimal point. For example:
10,302,321 -> 10.3 million or 10.3M 5,242,000,014 -> 5.2 billion or 5.2B 901,212 -> 901.2 thousand or 901.2K or 0.9M
For numbers with more than three digits, always separate each thousands place with a comma.
Use AP style when using numbers in copy. That is, spell out numbers under 10 except in the following circumstances:
Use figures for ages, sums of money, time of day, percentages, house numerals, years, days of month, degrees of temperature, proportions, votes, scores, speeds, time of races, dimensions and serial numbers. (via)
"Not available" and "not applicable" are abbreviated like this: N/A
Use AP abbreviations for states and avoid postal abbreviations except when the space is so constrained that you have to use them (such as in a table), or when the abbreviation will appear in all-caps.
We use the nytimes-style gem to help us abbreviate states correctly.
//Bad Practitioners in Golden, CO //Good Practitioners in Golden, Colo. //Bad 123 MAIN STREET, YOUNG AMERICA, MINN. //Good 123 MAIN STREET, YOUNG AMERICA, MN
Under every display of data, whether it's a map, chart, table or something else, show your data's sources. Do not list sources in the guff except in special circumstances.
Follow AP abbreviation style for dates, with one exception: Include the year in dates, even when the event described happened during the current year.
Months are abbreviated like this:
Jan., Feb., March, April, May, June, July, Aug., Sept., Oct., Nov., Dec.
Don't abbreviate months when used alone, or with a year alone, unless space constraints require it.
When including the time in a news app or graphic, abbreviate the meridian in AP Style: a.m. and p.m., with a space between the number and the meridian. We do not show minutes at the exact hour. For example:
7:31 p.m. 9 a.m.
We use the nytimes-style gem to help us format time correctly.
Put explanatory copy at the top of the first page of your app or graphic, under the byline. This copy goes by many names: "Lead-in," "top matter," etc. At ProPublica we call it "guff." It should be very short -- aim for no more than four or five lines. Avoid re-telling a whole news story, but do make sure you accomplish three things:
- Give the reader enough background to be able to understand the purpose of the app or graphic.
- Let the reader know how to start using any interactivity.
- Explain how to find the related story, if any.
Only use "total" as an adjective when it's not clear what you're totaling. Never use the redundant "total amount" -- just use "total."
Use a treemap to show data that is structured into hierarchical categories or classifications. A treemap is good at showing the relationship of each variable to its class and each class to a whole. The classic example is the stock market. Stocks are classified into industries and in turn into a whole market.
Complicated treemaps with many levels of classification should allow users to zoom in to each category and view the subdivisions within. If a treemap has only one zoom level, identifying information on categories and variables shown should be readable to the user immediately, and not hidden, for example, in a rollover.
Unlike an article, which tends to be a frozen description of a moment in time, news applications tend to be durable resources, and may need to be updated from time to time as new data becomes available.
When updating an app with new data, don't append a note explaining every change, as that note would be quite lengthy and very boring. Simply update the date in the byline to indicate when the data was last updated. If an app updates dynamically, the date in the byline should change dynamically as well.
Don't show both the original publication date and the most recent updated date in the byline. Your readers don't relish the archival history of our work quite like you might. Simply show the date of the latest update (after the word "updated," of course).
When the decision is reached to stop updating an app, put a prominent note on every page of the app that says when the app stopped being updated, and if possible, where to find more recent data.