The above picture shows where the notes on a C harmonica fall on a piano type keyboard. It can help as a visualization aid for those of us who picture notes as they are laid out on a piano. For keyboard players, it can help translate from piano/synth licks to harmonica licks. The positions are shown in circles above and below the keyboard graphic. Notice that as you proceed in whole steps, the position numbers increase by 2. Positions are sometimes specified based on the C harp, for example "Ab on a C harp" instead of 9th position, or even "1/2 step above cross harp".
However, when playing in 2nd position, the C harp is played in the key of G, which is not the simplest key in which to visualize music.
The picture below shows where the notes on an F harmonica fall on a keyboard. An F harp played in 2nd position is the key of C--the natural choice for thinking about musical relationships. For me, this is the best way to visualize the generic note layout for 2nd position on a diatonic harmonica. The colors show where the hole-numbers change. Light blue and dark blue go together, as do white and black. 2 draw and 3 blow are shown in both colors.
F Harp Layout on a Keyboard
This diagram is similar to the above one, but the coloring shows breath direction instead of by-hole. Blow notes are shown in shades of blue, while draw notes are shown in white, black, and gray. Overblows are shown in shades of red.