Datum planes are used as a reference on a part where a reference does not already exist. For example, you can sketch or place features on a datum plane when there is no other appropriate planar surface.

You can also use a datum plane as a reference to place set datum tag annotations. If no datum plane exists, selecting the planar surface to which the datum tag annotations are associated automatically creates an internal datum plane. The set datum tags are placed on the reference datum plane or the coplanar surface associated with the datum plane.

You can also dimension to a datum plane as if it were an edge. When you are constructing an assembly, you can use datums with assembly commands.

Datum planes are infinite, but you can size them to fit a part, feature, surface, edge, or axis, or specify values for the height and width of the display outlines of datum planes. Alternatively, you can use the handles that are displayed to drag the boundaries of datum planes to resize their display outline.

You can create a datum plane by specifying constraints that position it in relation to existing geometry. The constraints you choose must position the datum plane relative to the model without ambiguity.

By default, datum planes have two sides: brown and gray. You use the colors when you assemble components, orient views, and sketch references. Datum planes are displayed as brown or gray, depending on which side is facing the screen.

When you create datum planes, names are assigned in sequential order (DTM1, DTM2, and so on). If desired, you can set an initial name for a datum plane during the creation process by using the Properties tab in the Datum Plane dialog box. Or if you want to change the name of an existing datum plane, you can right-click the datum feature on the Model Tree and select Rename from the shortcut menu, or double-click the name of the datum plane on the Model Tree.

To select a datum plane, you can select its name, select one of its boundaries, or select it on the Model Tree.