A gauge widget depicts the value of a certain attribute or a count of features as a percentage of a target value; for example, a gauge might depict the unemployment rate for a layer of United States counties with census information. The target value in this case would be 100.
In many cases, gauges are more informative when the highlight value depicted by the gauge is below or exceeds a threshold value; for example, a gauge that depicts fuel level might have a threshold of 10 percent, where the color of the gauge's graphic and value text is displayed in a different color when the value is below this threshold. This is useful for drawing your attention when the information depicted by the gauge reaches some critical level.
When a single feature serves as the data source, the value for the chosen field is shown in the widget. If more than one feature is used, such as when there are multiple selected features, a summary operation is performed on the field values. The aggregate can be any one of the following:
In an emergency management scenario, you could configure a gauge widget to show the number of people who have had to relocate to an emergency shelter after an earthquake. In this gauge, the widget shows values below the target threshold in green, which occurs when there are fewer than 15,000 people total (a sum operation) in all of the area's shelter locations. The widget displays red if the total increases above that threshold value, which causes an alert to appear. The maximum number of people that can be accommodated in all shelters is 25,000.