Daylight saving in temporal data

Daylight saving time is the concept of shifting the clock by up to one hour in the summer months. There are several advantages to doing this, such as increased amount of daylight during business hours. The exact date for this time transition changes from place to place and from year to year. ArcGIS software allows you to specify the daylight saving time rules that were used when recording your data. This allows ArcGIS to properly integrate your data with other time-enabled data so that events are displayed in the correct sequence.

Learn more about setting the temporal reference on your data

Daylight saving time

When enabling time on your data, you can specify the data's temporal reference. The temporal reference includes information about daylight saving time in addition to the time zone. You can specify a temporal reference by picking a time zone from a predefined list and choosing whether or not the time values in your data were collected in daylight saving time under the Advanced settings on the Time tab of the Layer Properties dialog box. Each temporal reference is labeled with the name of the region where it is used.

Learn more about enabling time and setting time properties on your data

You can also choose to visualize your data in a different temporal reference. You can specify a temporal reference on the time slider by picking a time zone from a predefined list on the Time Display tab of the Time Slider Options dialog box. Also, here you can specify whether or not you want to adjust your display time to account for daylight saving time when you are visualizing data. By default, it is assumed that the time zone you want to visualize your data in honors daylight saving.

Learn more about setting the temporal reference for visualizing your data

By specifying the rules for daylight saving time, you allow ArcGIS to draw the data on the map at the appropriate time. You will most likely see the effects of daylight saving time when you are using multiple layers that have different rules for daylight saving time. For example, if you are using weather data from a satellite that is stored in Coordinated Universal Time (UTC), this data would not have any adjustment for daylight saving time because UTC does not adjust for daylight savings time. If you also have information about automobile accidents collected using Greenwich Mean Time (GMT), this data would include adjustments for daylight saving time. For half of the year, these two datasets would line up correctly without any adjustment. For the other half of the year, they would be an hour apart. To properly display the data during the summer, ArcGIS needs to know that the automobile accident data was recorded using daylight saving time rules so that it can be properly adjusted. This results in the accident data aligning properly with the weather data.