This field can be used to separate data points into categories. All data points with matching data in this field will be assigned to the same category. 

Once you have added data to this field, Category Colors section will be revealed in the Format Visual tab, allowing you to apply separate node colors for each category. 

In addition, adding data to the Category and Value fields will allow you to aggregate cluster node values and display them as mini-donut charts directly on the map. You can enable this feature with the Pie Chart on Nodes toggle in the Node Settings section.