You are prompted for the map to AND with. The result of the logical AND is stored in the present default map. All points in the default map that have a counterpart in the second map being zero will themselves be set to zero. This option requires that the two maps have identical number of grid points, same origin and same grid spacing. This option makes the average of the default map zero.
Convex points are grid points that form a sharp external protrusion in the map.
They have more empty than filled points around them. In practice they are defined as points in the shell with three or more orthogonal neighbors that have the value zero. The option got its name because it removes the points that are at a convex surface. This option only works well on WHAT IF generated maps, or maps scaled such that the values fall in the 0 till 100 range. Other maps will cause this option to produce strange error messages.