Time series graphs can be used to visualize trends in counts or numerical values over time. Because date and time information is continuous categorical data (expressed as a range of values), points are plotted along the x-axis and connected by a continuous line. Missing data is displayed with a dashed line.
Time series graphs can answer questions about your data, such as: How does the trend change over time?
A crime analyst is studying crime trends in his city to determine if initiatives to reduce crime have been effective. The analyst uses a time series graph and compares the number of incidents over time to the timing of the crime reduction programs.
The graph above shows peaks in incidents in the period from May, 2014 to October, 2014 and again from May, 2015 to September, 2015. There is a decrease in incidents in February, 2014 and 2015. If the crime reduction programs occurred in those months, that would imply that the programs were effective, but only for a limited time.
The analyst realizes that looking at a total number of incidents over the two years only tells part of the story. Subgrouping the time series graph by another field, such as the crime type, can give more insight into the effectiveness of the programs for different types of incidents.
The grouped time series graph above indicates that the majority of incidents were categorized as Larceny. The counts of larceny show a similar pattern to the ungrouped time series. The other incident types, burglary, motor vehicle theft, and robbery, have relatively stable counts across the two year time period, with the exception of a spike in burglaries in May, 2015. Based on what the analyst sees in the grouped time series graph, he will recommend focusing the programming on reducing the number of larceny crimes in the city.
The following cards may be helpful to pair with your grouped time series graph:
- A related map styled with the same field you used to group your time series graph, such as Day Of Week. When you interact with the time series graph or the map, you'll be able to see simultaneous temporal, categorical, and spatial patterns.
- A related bar chart using the field you used to group your time series graph to see highest and lowest values by your chart subgroup.
Create a time series graph
To create a time series graph, complete the following steps:
- Select one of the following data options:
- A date/time field
- A date/time field plus a number or rate/ratio field
If you do not select a number or rate/ratio field, your data will be aggregated and a count will be displayed.
- Create the time series graph using the following steps:
- Drag the selected fields to a new card.
- Drop the selected fields on the Time Series drop zone.
You can also create charts using the Chart menu above the data pane or the Visualization type button on an existing card. For the Chart menu, only charts that are compatible with your data selection will be enabled. For the Visualization type menu, only compatible visualizations (including maps, charts, or tables) will be displayed.
Time series graphs can also be created using Time Series, which is accessed from the Action button under Find answers > How has it changed?
When you drag a date/time field onto your page, the Chart drop zone is replaced with the Time Series drop zone. The reason for the change is because a time series graph is the only chart type that can be created using a date/time field.
By default, time series graphs are symbolized using a single symbol. You can change the Chart Color using the Legend button . You can add a string field to the Subgroup variable on the x-axis to change the time series to Unique symbols. The Subgroup variable must be a string field and will be used to divide the time series into subcategories. If unique symbols are used, the legend can be used to select data on the time series graph. To change the color associated with a category, click the symbol and choose a color from the palette or enter a hex value.
The trends for the time series graph can be symbolized as a count of features over time or as a number or rate/ratio field. If a field is used, the values in the trend line can be calculated as the sum, minimum, maximum, average, percentile, or median of values from the field for each point in time.
Median and percentile are not available for remote feature layers.
Use the Chart statistics button to display the mean, median, upper quartile, lower quartile, or a custom value.
Click on the y-axis to switch the scale between Linear and Log.