Nikon D6 Reference Manual page 155

Option
[Group-area AF]/
[Group-area AF
(C1)]/[Group-area
AF (C2)]
[Auto-area AF]
The camera focuses using a group of focus points
selected by the user.
•
Choose for snapshots, subjects that are in motion,
and other subjects that are difficult to
photograph using [Single-point AF].
•
Use [Group-area AF (C1)] and [Group-area AF
(C2)] to create custom groups in which the
number of focus points in each dimension can be
chosen using the multi selector. This can be used,
for example, if the size and shape of the area used
for focus can be determined in advance with a fair
degree of accuracy.
The camera
automatically detects
the subject and selects
the focus point. If a face
is detected, the camera
will give priority to the
portrait subject.
Description
The AF-Mode Button
103