System mapping is the process of making a model of your system in some way.
Many systems make system maps. A system list is a system map in one of its simplest forms, but there are a lot of other kinds of system maps that people might make to get more information. Some system maps might show internal structure and lines of communication. Some show relationships or opinions. Some show common themes and differences between system members. Etc.
There's really no wrong way to make a map. What matters is that the map is useful to you- it should give you information that helps you work with your system better. It might give you a better understanding of why your system works the way it does, or it might tell you who might need support or who might need to work on establishing communication.
Communication
Sometimes, it can be useful to map out who in your system can talk to whom. This is a very simple kind of map to make, and it gives you useful information about your system that ranges from "huh, these two can't reach each other" to "there's a gap here- are we missing someone?"
Lay out every known system member on a piece of paper. If two people can talk to each other, draw a line between them. If the communication is one-way only, draw an arrow. If two people can't reach each other, don't connect them. If two people can reach each other indirectly but you don't know who's linking them together like that, draw a line with a gap in it.
You might also add dotted lines for weak or unreliable communication, or other kinds of lines for other special cases.
Relationship
It can be helpful to know how different system members get along (or don't). Relationships in a system can be mapped with something similar to a shipping diagram, and looking at the resulting map can make it very obvious if someone is overall liked, disliked, rejected, etc. It can also point out interesting patterns in who gets along and who doesn't.
Draw your system members arranged in a circle. Then, draw color-coded (or otherwise coded- make a key) lines between members that like each other, dislike each other, or have other important opinions about each other.
Structure
Sometimes, drawing the arrangement of your system can teach you how to work with it better.
If two people feel close to each other (e.g. they may have unusually easy communication, common interests or themes, common issues, etc.), then draw them close together. If two people feel far apart (e.g. poor communication, lots of differences and disagreements, don't really understand each other), then draw them far apart.
By the end of this, you have a map that shows you which people are clustered together and which people are disconnected, rejected, or otherwise pushed away. This can be very useful when trying to bring any cast-out people closer to the rest of your group, as it can make isolation very obvious.
You can also map other aspects of system structure. For example, you might consider mapping the relationship between the different places that people can occupy in your system (front, back, etc.):
This kind of map can be very abstract sometimes. We have a few structure maps that we've made over the years, and they probably don't make a ton of sense to people that aren't in our group, but they've helped us a lot.
You might also consider mapping associations. What colors are associated with your system members? Do they have common themes or imagery? Does everyone associated with the color green have a hard time talking to people associated with blue? Are powerful people usually associated with certain species?
Timeline
Sometimes, it can be helpful to make a timeline of important life events that happened to your group. If you have guesses about when some people showed up or changed, then putting those dates on the timeline can give you insight into what those people might be dealing with.
Content warning for trauma, suicide and egocide, and general unpleasantry if you read this one. We censored the most sensitive parts (and those we'd simply prefer to keep private), but it's still heavier than the other maps in this post.
Headspace
If your headspace is possible to map, then sometimes mapping it can teach you something about your system. It doesn't have to be very detailed to help, nor does it have to be entirely logical.
We don't have the one headspace map we've made in easy reach, unfortunately, and it's out of date. That said, conventional land mapping tricks will often work for places in headspace. Recreating headspace in a game like The Sims or Minecraft is also an option.
If multiple places overlap, then consider making a pop-up map or otherwise representing that overlap- it can be useful information. Likewise, if parts of headspace correspond to parts of your body or parts of your system, then it can be helpful to make a note about that.
Adapting for Large and Complex Systems
Larger systems may not all fit on one piece of paper. Complex systems may not fit on a 2D surface at all- there might be layers involved that need a 3D surface. System mapping still works for these cases, but you may need to approach it a little differently.
Try mapping your system's subgroups instead of individual people.
Try making multiple maps for different "regions" of the system. Consider including information on how those maps connect together.
Make good use of color coding and keys to pack more information into a smaller space.
Try mapping by using digital drawing programs and tools. A digital canvas can be much larger than a physical one.
Try mapping in 3D. Make a sculpture, stack sheets of paper, fold the paper, use the back side, draw a 3D shape, and experiment with other ways of arranging the map to better reflect your situation.
Use multiple kinds of map. Each map is likely to have part of the overall picture, and looking at them together is likely to give you useful information about how it all fits together.
Finally: system mapping is not required. It can be helpful for some systems, but it won't work for everyone, and some systems find that it harms them or makes their lives harder to live. If mapping doesn't work for you, then that's okay- there are plenty of other ways to get to know your system better. Do what works.