Animators often talk about how their characters are "rigged". Essentially, this means how the parts of the character they are creating fit together using a system of "rigging", like the rigging of sails on a ship.
Character rigging comes from 3D animation, in which the parts of the characters are manipulated by "rigs" of external control devices, usually referred to as "bones" much as the bones control the human body. Move an arm bone in such a rig and the arm moves (hopefully naturally).
It's much less common to talk about rigging a 2D character, but certain animation systems allow such a control system. In Anime Studio (which we use for all our animation) there is such a bone system almost identical to those in 3D programs (although, obviously, it will only move and deform in 2 dimensions).
To use this effectively we need to create our character parts so they can be manipulated properly and the above image is the way that we do it. It's not the only way, nor is it necessarily the best, but it works for us.
Each of the major body parts is put on a separate layer. Once again, this isn't the only way to do it, but it does mean that parts such as the arms can be moved in front or back of other parts, like the head, for different effects. If they were all on the same layer this would be extremely difficult.
There are other things to note: this character is drawn in 3/4 view, as all all of our characters. This kind of "American Dad/Family Guy" style basically mimics the "cheat" that an actor in a play does as they turn slightly to open their body up to the audience while at the same time interacting with other actors on stage. Next time you watch a play notice that this 3/4 position is the one they maintain at almost all times (the old stage adage is "never turn your back on an audience -- they might start to throw things" :>)
It's also worth noting that the downstage arm is finished straight across at the top -- this allows it to rotate freely within the shoulder while not showing any bad edges. The upstage arm is finished because the shoulder part will be partially hidden by the body.
We'll talk about the actual bones and how they control things in a future post.