Features

A. Chart Elements

1. Insights

An Insight is an author-written text-based description of an element of a visualization rendered with Chart Reader. Each Insight is composed of the following: a title, a description, a type/group, and a pointer to the specific data points within the visualization which it describes.

Within the chart structure, the Insights are a first-level element (sibling to X-Axis, Y-Axis, Data Points, and Filters). The Insights element is structured as a list of Insight Groups, each related to a distinct type of information. The first Insight in all charts is the Summary Insight , summarizing the visualization and prominent features or trends the author wants to highlight. The Summary Insight is also used as the top-level “alt text” of the interactive chart before the user begins interaction.

Aside from the Summary Insight, all Insight Groups are fully customizable to the chart author.

In our implementation, we included the following Insight Groups for single-series and multi-series line charts:

Trend Insights , which describe prominent trends and relationships between series in the chart
Landmark Insights , which describe notable features in the chart, such as local maxima & minima
Statistical Insights , which provide information about the maximum, minimum, average, and standard deviation of each series

In our implementation, we included the following Insight Groups for stacked bar charts:

Comparison Insights , which describe relationships between sectors in the chart
Series Ranking Insights , each of which presents the rankings for a series, listing each category’s ranking in the series from highest value to lowest value
Statistical Insights , each of which presents a category’s rankings across all series

Each individual insight is linked to the relevant portions of data within the chart. By pressing ENTER to progress down a level in the hierarchy, users can navigate directly to this linked data, navigating them to a subregion of the Data Points.

There is no Sonification available for the Insights element, Insight Groups, or individual Insights.

2. X-Axis

The X-Axis of the chart is a first-level element (sibling to Insights, Y-Axis, Data Points, and Filters). When focused, it provides a verbal description of the chart’s X-Axis, consisting of the units, the maximum & minimum, and the size and count of its bins (described below). From the X-Axis, the user can navigate down a level to the list of X-Axis Bins.

There is no sonification available for the X-Axis.

X-Axis Bins

The X-Axis is split into an author-defined amount of subregions called X-Axis Bins. All bins within a given chart are the same size, with the exception of the first and last bin, which can be trimmed to account for partial data. (For instance, if a chart has bins that each represent one year and contain a data point for each month, a final bin could be trimmed if the data ends in March of a given year.)

When focused, each bin lists the average value for each series within the span of the bin, ordered from lowest average to highest average.

When sonified, a bin plays a tone for the average value of each series within the span of the bin. These tones are spatialized to enable easier distinguishing between series.

When navigating down a level from an X-Axis Bin, the user is brought to a subregion of the Data Points that includes all data points within the span of the X-Axis Bin.

3. Y-Axis

The Y-Axis of the chart is a first-level element (sibling to Insights, X-Axis, Data Points, and Filters). When focused, it provides a verbal description of the chart’s Y-Axis, consisting of the units, the maximum & minimum, and the size and count of its bins (described below). From the Y-Axis, the user can navigate down a level to the list of Y-Axis Bins.

There is no sonification available for the Y-Axis.

Y-Axis Bins

The Y-Axis is split into an author-defined amount of subregions called Y-Axis Bins. All bins within a given chart are the same size.

When focused, each bin lists the percentage of each series’ data points that fall within that range. (For instance, if there is a bin representing values 0-100, and 25% of all points of Series A are between 0 and 100, 25% will be read out for Series A.) If 0% of a series’ data points fall within the range, the series will not be announced.

There is no sonification available for Y-Axis Bins.

When navigating down a level from a Y-Axis Bin, a user is brought to a list of subregions of the Data Points that represent continuous spans of data within the given Y-Axis Bin.

If a Y-Axis Bin has no data points within it, the user will not be able to navigate down a level (as there are no spans of data) and will hear a Boundary Tone.

4. Data Points

The Data Points Region element is a first-level element (sibling to Insights, X-Axis, Y-Axis, and Filters).

No additional description is provided when the Data Points Region is focused.

There is no sonification available for the Data Points Region.

Individual Data Points

From the Data Points Region, users can navigate down a level to the individual data points. The individual data points are structured as a group of lists of points, where each list of points represents a Series with its points ordered from lowest X-value to highest X-value.

From a given individual data point, a user can navigate to the data point for the preceding or following X-value within that series, or they can navigate to the data point for the same X-value in a neighboring series. Series are ordered based on average Y-value.

(Note: This organizational structure can be loosely interpreted as a 2-D array or grid structure, though this is not a perfect metaphor: the first and final Series are neighboring to each other, but the the first and final points of a given Series are not neighboring to each other, so it is best described as a 2-D array with wraparound in a single dimension. For a visual depiction of this, consult Figure 3 within the paper.)

When focused, an individual data point announces its Y-value, its X-value, and its Series. These values are ordered by which most recently changed: if a user is navigating within a series, the Series will be announced last; if a user is navigating across series at a given X-value, the X-value will be announced last.

When sonified, an individual data point will play a tone corresponding to its Y-value. The user is also able to sonify a full series, automating playthrough of all following individual data points for a selected series, starting at the currently selected point.

Data Point Subregions

In some cases, a user can navigate to individual data points from a location in the chart other than the Data Points Region, such as when they move a level down from an Insight or a Y-Axis Bin. In these cases, the user’s navigation is constrained to only the data points determined by that subregion; even if there are adjacent data points, the user cannot navigate past the boundary of the subregion. This is intended to make it easier to understand what data is included within the subregion.

When inside a subregion, navigating up a level in the hierarchy will return the user to where they entered the subregion from, rather than navigating them to the Data Points Region.

5. Filters

The Filters Region is a first-level element (sibling to Insights, X-Axis, Y-Axis, and Data Points).

When a user navigates down from the Filters Region, they access the list of individual Filters within the chart. These filters are a list of toggleable checkboxes that determine whether a series’ data will be included in the rest of the chart.

No additional information is provided when focused on the Filters Region or individual Filters .

There is no sonification available for the Filters Region or individual Filters.

6. Series Comparison (Multi-Series Charts Only)

In multi-series charts, Series Comparison is a first-level element (sibling to Insights, X-Axis, Y-Axis, Data Points, and Filters). This element exists solely to enable Multi-series Spatial Sonification.

When in Series Comparison, the user can navigate down a level to an interactive X-Axis that allows them to specify an X-value for Multi-series Spatial Sonification.

No additional information is provided when focused on Series Comparison or its interactive X-Axis.

There is no sonification available when focused on Series Comparison.

B. Interactions

1. Sonification

Pointwise Sonification

Pointwise Sonification is available when focused on an individual data point. When triggered, a single, discrete tone will be played to indicate the Y-value of the data point.

To trigger pointwise sonification, hold down SHIFT while navigating to an individual data point. The full list of data navigation controls can be found here.

Single-series Sonification

Single-series Sonification is available when focused on an individual data point. When triggered, a sequence of tones will be played indicating the Y-value of each consecutive data point within the series, starting at the currently focused data point and continuing positively along the X-axis.

The sonification stops when the end of the series is reached, or if the user manually stops the sonification. In either case, focus will shift to the most recently sonified data point.

To trigger single-series sonification, press SHIFT+ENTER while focused on an individual data point. To stop sonification early, press SHIFT+ENTER again.

Multi-series Spatial Sonification

When in Series Comparison for a multi-series line chart, multi-series spatial sonification replaces pointwise and single-series sonification. Note that this mode requires the use of stereo audio or a similar 3D audio setup.

When using multi-series spatial sonification, each series is assigned to a location in 3D audio space. The first series will always be assigned as “Left”, the final series will always be assigned as “Right”, and all other series will be evenly spaced between Left & Right.

When navigating using Pointwise Sonification in this mode, instead of a single tone being played for a currently focused point, a tone will be played for each series at the currently focused X-value. Tones will be played discretely (i.e., not as a chord) in series order (i.e., from Left to Right).

When playing a Series Sonification in this mode, a tone will be played for each series at each consecutive X-value, starting at the currently focused X-value. Tones are played discretely & in series order, and there is a slight pause before progressing from the final tone of an X-value to the first tone of the following X-value.

X-Axis Bin Sonification

When focused on an X-Axis Bin, pointwise and series sonification are replaced by X-Axis Bin sonification.

When using pointwise sonification on an X-Axis Bin, a tone is played denoting the average value for the series within that bin. If in a multi-series line chart or a stacked bar chart, a tone will be played for the value of each series within the bin. Tones are played discretely & in series order. (Note: if using spatial audio, these tones will also be spatialized, as described here).

When using series sonification (i.e., pressing SHIFT+ENTER) on an X-Axis Bin, the current X-Axis Bin will be sonified as if using pointwise sonification, and then each subsequent X-Axis Bin will also be sonified. When the sonification finishes or if the sonification is interrupted by the user, focus will shift to the most recently sonified X-Axis Bin.

2. Earcons

Boundary Collisions

If the user attempts an invalid navigation action (such as pressing RIGHT while focused on the final data point in a series), a “boundary collision” earcon is played to indicate that the user cannot navigate in that direction. This earcon sounds like a cartoon “bonk” noise.

Invalid Sonifications

If the user attempts to play a sonification (either pointwise or series) when focused on an element that cannot be sonified (such as a Filter or Insight), an “invalid sonification” earcon is played to register that the input was received but that there is no sonification to play. This earcon sounds like a water dripping noise.

3. Document Mode

When focused on an element with a textual description, the user can press SPACE to activate Document Mode. When in document mode, the user can navigate through the text using their screen reader’s standard text navigation. When in Document Mode, other keyboard controls will not be processed by Chart Reader. To exit Document Mode, the user can press SPACE again, and they will be re-focused on the element they were focused on when they entered Document Mode.

The following controls can be used anywhere throughout the chart experience:

Command	Action
`ENTER`	Navigate one level lower in the hierarchy (“Drill Down”)
`ESCAPE`	Navigate one level higher in the hierarchy (“Drill Up”)
`TAB`	Exit the Chart
`SPACE`	Enter/Exit Document Mode
`RIGHT`	Navigate to the next sibling element on this level of the hierarchy
`LEFT`	Navigate to the previous sibling element on this level of the hierarchy
`HOME`	Navigate to the first element on this level of the hierarchy
`END`	Navigate to the final element on this level of the hierarchy
`PAGE UP`	Navigate 5 elements forward on this level of the hierarchy
`PAGE DOWN`	Navigate 5 elements backwards on this level of the hierarchy

The following controls are added when focused on individual data points:

Command	Action
`UP`	Navigate to the next series (multi-series charts only)
`DOWN`	Navigate to the previous series (multi-series charts only)
`INSERT`	Re-announce / re-focus on the currently focused data point

3. Sonification Controls