Calendar aggregation is a topic that will come up time and time again when discussing desired functionality for a collaborative environment. Outlook 2007 introduced the ability to view multiple calendars side-by-side or overlaid and users have grown comfortable with the idea that they can see many people's schedules and availability in one simple view. During the planning phase of a SharePoint intranet, or even when talking to organizations that have been using SharePoint for a while, I often hear the question: “How can I view multiple calendars in one place in SharePoint?” Prior to SharePoint 2010 this could not be achieved without custom development, which is not always ideal or even an option for some organizations. A workaround for this is to create multiple calendars in SharePoint, connect to them in Outlook and then use Outlook to overlay the calendars. This means that although the aggregated SharePoint calendar view is available, the user has to go outside of SharePoint to get it, defeating a key purpose of the intranet or portal: facilitate collaboration, access to information, data, and utilities in one location.
SharePoint 2010 introduces the Calendars Overlay feature, available out-of-the-box on all calendars. This feature enables the ability to add up to 10 SharePoint calendars as overlays, each calendar identified with a different color (which the user can select). Configuration of this feature is easy – after creating the calendar, you can find the Calendars Overlay button on Calendar tab of the ribbon.
Clicking this button will open up a new page where you can select the overlay calendars. They must already exist in SharePoint prior to this activity.
Once the overlay has been added, all events belonging to that calendar will be displayed in the selected color.
Due to the limitation of 10 overlay calendars, this may not be the perfect solution for every situation. It is, however, a huge improvement to the calendar functionality that we were used to working with in 2007.