You can specify what to show in a forecasting report with Dimensions. Dimensions determine how to split the report:
TAP Impressions: Position is the default. You can include up to 2 more Dimensions.
TAP Spots: Only one dimension, Station.
TAP Reach Extension: Inventory Owner is the default. You can include up to 2 more Dimensions.
Select Dimensions

To change the default dimension, select it and then select a different one from the Edit Split panel. To include another dimension, click Add New in the Dimensions section to open the Create New Split panel on the right. Choose a dimension from the list and click Save.
Dimension Order
The order in which you include dimensions affects how the data is presented. The report shows avails split by the first dimension and further split by the next dimensions.
The following examples show a TAP Impressions report with Filters for pre-roll and mid-roll positions for two station/podcasts and the iOS and Android operating systems with Dimensions for Position, Station, and Operating System.
Example: Position > Station > Operating System

All mid-roll inventory.
Mid-roll inventory for this podcast.
Mid-roll iOS inventory for this podcast.
All pre-roll inventory.
Pre-roll inventory for this podcast.
Pre-roll iOS inventory for this podcast.
Example: Position > Operating System > Station

All mid-roll inventory.
Mid-roll iOS inventory.
Mid-roll iOS inventory for this podcast.
All pre-roll inventory.
Pre-roll iOS inventory.
Pre-roll iOS inventory for this podcast.