Pie chart symbols are used in maps to show the proportions of categorical data associated with a single feature, using either a count or a summary statistic. Pie chart symbols are created on a map using a string field and a location field containing coincident values.
Pie chart symbols can answer questions about data, such as the following:
- What are the proportions of categories for each feature?
- What is the count or summary statistic relative to another location?
An insurance company is reviewing purchases of its policies across the United States to determine where there is market potential for each policy class (automobile, disability, life, and property). The analyst in charge of the review joins the insurance portfolio data for the company with a state boundary layer and uses the result to create pie chart symbols showing the proportions of each policy class that are being purchased in each state, with each pie chart sized by the number of policies in the state.
The analyst can use associated charts, filters, or the map legend to determine which states have potential for each policy class. The analyst selects automobile policies and sees that there is low automobile insurance uptake across the Midwest. The analyst will do more research to determine why there are states with low or no automobile insurance uptake (for example, is automobile insurance not offered, or is there a major regional competitor?) and whether there is potential to increase uptake in those states.
Create pie chart symbols on a map
Pie chart symbols can only be created with multipart datasets in which features are collocated. These datasets can be created using a one-to-many join, or by enabling location on a dataset. If location is enabled with addresses or coordinates, Repeat identical features must remain unselected.
Use the following steps to create a map with pie chart symbols:
- Create a multipart dataset using one of the following methods:
Create a join between two datasets. Generally, these datasets will include the features you want to display as pie chart symbols and a boundary layer.
The join should be one-to-many, meaning each boundary feature contains more than one feature to create the pie chart. In the example above, a join was created between a dataset with insurance data and state boundaries.
Enable location for your dataset.
If you enable location for points using addresses or coordinates, Repeat identical features must remain unselected. This method should only be used in situations where multiple data points appear in the exact same location. For example, a dataset containing monthly status updates for fire hydrants in a city could contain a new input each month for each fire hydrant. Enabling location without repeating identical features will aggregate the inputs for each hydrant.
If you enable location using geography, there should be multiple features within each boundary. This method functions the same as a one-to-many join.
- Expand a dataset in the data pane so that the fields are visible.
- Select one of the following combinations of fields:
- A location field plus a string field
- A location field, a string field, and a number or rate/ratio field
If you created a join in step 1, the location field you select must be the field that corresponds to the boundaries.
You can search for fields using the search bar in the data pane.
- Drag the fields to the page and drop them on the Map drop zone.
A unique values map is created using Types (Unique Symbols) as the Symbol Type.
- Expand the legend to display the Layer options pane.
- Browse to the Options tab .
- Change Symbol type to Pies.
The Layer options pane is accessible from the layer legend and can be used to view the classification values being mapped, change the style of the map, and view information about selected features.
Use the Legend tab to view the values and counts of the pie chart symbols and make selections based on the values. To change the color associated with a category, click the symbol and choose a color from the palette, or enter a hex value.
Use the Options tab to do the following:
- Change the field displayed on the map, or switch to a different type of map.
- Change the numeric variable. The numeric variable divides the pie chart into proportional segments and can be based on a count of features or a number or rate/ratio field. If a number or rate/ratio field is chosen, the proportions can be based on a sum, minimum, maximum, or average.
- Change the classification type (natural breaks, equal interval, or unclassed).
- Change the number of classes displayed.
- Configure the map pop-ups to display with or without statistics, or disable pop-ups for the layer.
Use the Style tab to change the symbol style properties, such as symbol size, outline style, and layer transparency.
Use the Attributes tab to view details for features selected on the map.
Pie chart symbols show all unique categories associated with a single feature or location. If the features contain many unique categories, the pie chart symbols may be difficult to interpret.