Most simply put, an internal landscape is a shared mental refuge for DID systems. An internal reality. An internal world.
In some cases it's a literal copy of external places, an internal adaptation of a known location in which the plural or multiple's system members can interact.
Popular sayings like "a corner of my mind" can be taken much more literally when it comes to DID. We really can have a corner of our mind, an "in our head".
Subjectively speaking, the internal landscape can be as real as (or even more real than) external reality. The internal landscape or internal reality can be used as a metaphor and is usually fairly easily adapted and modified. It can be a world all its own, open for exploration.
To find your internal landscape, one might ask "Where do I go when someone else comes out?" or even "Where are those other voices coming from?" Some headmaps describe the internal landscape rather than an organizational diagram of the relationships, the internal landscape can describe those relationships between those on the inside by where they live in what looks like a building diagram or a map.
More complicated systems can have entirely separated communities within their internal landscape, representing sub-systems. They may have emissaries, ambassadors between these distinct communities in order to communicate and negotiate agreements.
By residents, in many ways we're talking about those who reside in your system's internal landscape.
Internal landscaping is the act of deliberately influencing or crafting your internal landscape for any reason. Sometimes in therapy, you'll be asked to create a meeting space in your internal landscape, so that you can invite other residents to a meeting. Or you may want to use or modify your internal landscape on your own as part of self-help, such as mentioned in these self-help articles on internal landscaping.
Features of Internal Landscapes
There are internal landscape "boundaries". These are structures that serve to segregate people &/or information in a system. These translate to fixed hard boundaries (for example walls), permeable boundaries (doors, windows, gates, fences, etc.), and broken boundaries (a demolished wall, broken door, etc.). These can be seen as metaphors, but working with them can be very effective in changing the relationships in the system.
Some things in an internal landscape are just "there" and have no function. They're cosmetic. Like wallpaper — it looks pretty, but it doesn't do anything. It's simply an ornamental fixture.
Other things have a purpose. A telephone. There's some corner of a multiple's psyche that is activated when they interact with these items, so we consider them functional fragments.
Then there are programmed constructs, which serve to actually process and change something, or detect input and execute a reaction (see Implementation Intentions for research into temporary constructs).
!Stub - to be continued. Sorry