The charted area shows the combination of geographic areas with variables and metrics up to the most complete month of data. You can toggle charted items on and off in the legend. You can select anywhere on a line or bar to see individual values, and you can see the variable elements for each chart just below the x axis.
Line charts will not show values on the line until selected, whereas bar charts will always show values. When selected, whether a line or bar chart, the date, area and value will display. Data points are for one month of activity or for 12 months of activity as a single point, depending on whether Monthly or 12 Months is the chosen time calculation, the latter of which is better for trend analysis and accounting for small sample sizes.
Bar charts will show percent changes for the years in which all data used to calculate the percent change is displayed in the chart. So, yes, that empty space is on purpose under the first year of any multiyear selection and for a time calculation set to 1 Year.
The chart’s heading is the selected metric or metric + variable when in variable breakout mode. The legend shows areas or areas + variables in variable breakout mode. Below the chart are areas with variables or areas with nonbreakout variables in variable breakout mode. Metrics, areas and variables also transfer to Share options.
For all charts, the y-axis is based on the metric, the x-axis is time of year and there are never more than six variables on a single chart. For bar charts only, the maximum allowable number of years for historical comparison is three. Beyond that, you really should be using a line chart!
If a line or bar doesn’t have any data, a “No Data” note will be added to the legend label. If there is no data for anything selected, a message will appear in the chart area that states, “There is no data available to display for the given criteria.” Different verbiage may appear in no-data situations, but the message is generally the same: No dice; try again.