Canon EOS-1D X Mark III Af Setting Manualbook page 42

Choose whether only one AF point is
used, or select from a wider area of AF
selection options
The EOS-1D X Mark III is equipped with up to 191 AF
points when using the viewfinder. When Live View is used,
you can select an AF point within the up to approximately
90% horizontal and 100% vertical area of the image. Not
only can all these AF points each be selected individually,
they can also automatically switch between multiple AF
points within a wide area to track the subject. The "AF
area selection mode" and "AF method" setting allows
the selection of these AF point modes.
The two types of modes in which you can manually select
a single AF point to focus with are [Spot AF] and [1-point
AF]. There are modes that can capture the subject in a
wider area [AF point expansion (manual selection
point expansion (eight surrounding points)], [Zone AF],
[Large zone AF (vertical and horizontal can be selected for
Live View)], [Auto selection AF (only during viewfinder
shooting)], and [
shooting)].
Mode features are explained on pages P. 47 - 63, so you
can select the mode best suited to your subject's
characteristics and shooting scene.
+ Tracking (only during Live View
42 42
)], [AF