Available with 3D Analyst license.
Anchor points remain through all pyramid levels of a terrain dataset. They are never filtered or thinned away. This ensures they are present in the terrain surface regardless of what resolution pyramid level is being used. This applies to both display and analysis operations.
The intent of anchor point support is to provide the option to preserve a relatively small collection of important measurements, such as control points, benchmarks, and "golden" soundings, in the terrain at all times. An example application is navigation safety, where a generalized pyramid level can be used for analysis with the assurance that critical mountain peaks (for air) or shallow features (for water) are in the surface model and have not been filtered out along with other less critical information.
A point feature class can be assigned the anchor property when it's added to a terrain dataset. Multipoint feature classes are not supported as anchor points due to the size that multipoint feature classes can reach. To change this property you can remove and add the feature class again using a different setting.
Setting Anchor points
In the New Terrain wizard, a point feature class can be set as Anchor Points in the Select Feature Class characteristics options on the New Terrain dialog box as shown in the following example.