Try to summarize thread idea to something logic.
General goal: keep fortress population by immigration and emigration. Without any population cap. Probably cap might be useful in some situations (roleplay, tests, etc.), but generally - only by migration.
Any dwarf have new scale "sedentism". Don't know is it really good title... Express dwarf's desire about migration. It split on three general states: "high" - dwarf want to stay in settlement, "middle/neutral" - there is some question about in his/her mind, "low" - dwarf want to leave settlement.
In "neutral" state dwarf "thinking" about leaving but do nothing of that.
In "low" state dwarf seeking opportunity to leave fortress. In general this state is similar to strange mood. Dwarf will be unhappy from any lost chance, in the end - tantrum or suicide (with very low sedentism scale and unhappiness). The difference is dwarf works as usual, except more long breaks, more drank booze.
New status: migrant. You have no control upon creature. There is no impression on sedentism. They don't work and usually gather in meeting areas or around other migrants. May steal food/drinks, if they lack of it (and it's possible for creature to filch, according to treats). This is a crime, so your police can arrest them and keep in cages
Emigration.
How your emigrants might leave you:
- Trade caravan. Of course leaving map (by most part) alive. And if there are free of any danger path to them (even through closed doors, bridges, etc.). In case of no path (walls, rivers, other interesting things) to caravan, this counts as "lost chance" and minus.
If caravan is on trade deport - dwarf will try to go to them and join. If caravan didn't reach your trade deport, when they say, they are soon to leave, dwarf will try to join them immediately. When dwarf is adopted by caravan, he/she becomes migrant.
About danger: dwarf looking on environment around his path, if there are dangerous creatures on every way - alas, you ought to stay here. No influence on sedentism in this chance.
Caravan can refuse your dwarf, there may be many reasons like
- Race (elves - 70-90% refuse, humans - 30-50%, dwarf - also a few percent, for example)
- Political relationships (war - near 100% refuse), if they are exiles - they take anyone with happiness, etc. Might override previous point.
- Outdoor dangers. siege, wolfs, titans - all is ok, at least Urist may feed wolfs... But minus for necromancer and some evil biomes - there is no need in more one zombie. Might override previous points.
- Dwarf profession. One more soldier? You are welcome. Legendary smith? We will be pleased by your joining! Might override previous points.
- Too many migrants. Traders are not service of transporting people... (max 3-5) Might override previous points.
- Expedition of emigrants. Expedition may contain any persons looking for leaving your fortress. They will try to organize "expedition".
Expedition includes: expedition leader, sentinels, non-conflict collective.
They take along: some food, booze, cloth, work instruments, some of their belongings, probably a few valuables. Soldiers take their 'native' armor and gear. Leader don't need any social profession (but preferable) though must fit traits. Guards are essential, and there are lower bound depending on risk outside. Races there might be mixed (with absence of conflicts, of course). Some persons may not like obey other race's leader.
Forming. Needs at least leader candidate and one more creature. Otherwise (without leader or only one) they will just seek opportunities. Leader and all other members need not to be in (near) panic state (see below), tantrum, melancholy, strange mood.
While expedition is being formed, all dwarf which are a part of expedition become migrants. They gather in certain place (usually in meeting hall and don't change it while it's available!) and start preparing. Any fit dwarf can join any time.
There appears new scale: readiness of expedition. Includes: stuff (food, drink, cloths) and guards. More their desire to leave (less their sedintism), then lower edge of readiness. When readiness if higher then edge - expedition is ready to leave and tries to go out. From that moment it counts as "chance of leaving" for anyone among their numbers. Expedition don't adopt anyone starting from this moment.
They leave fortress only in full numbers (except dead/badly injured) and don't return in case of lack of something (guardians too).
All members lowers their sedentism, while preparing expedition, but bonus disappears with time, if expedition abandoned by this dwarf. That may cause drop of expedition or certain dwarfs.
- Party of emigrants. Basically it's like expedition, but: no leader, guards are not essential, all dwarfs have friendly, family or trustworthy relationships (not in-game term, it might depend on traits and in-game relationships). They take the same stuff as expedition in moment of leaving (no long preparations) and leave. Minimal size of party depends of outdoor danger, self-defense and sedentism rate.
Like to be with family/friends in one party and may wait some time for them. Might push out strangers in tendency to add friend/family member.
Rarely leave fortress alone.
- Panic flee. This is for person, who has: too low happiness, too low sedentism. They have one general thought: to go out of here. May abandon their belongings, pets, try to run through dangerous creatures (goblins, etc.). Also may try to escape through caves.
Have migrant status.
-Near panic state: dwarf wandering around, don't work (eat, sleep, drink), probably have migrant status, chaotic draw items, etc.
Immigration.
There is some improvements.
Immigrants have migrant status. For 1-2 weeks - this dwarfs are "looking around". After the time any of them, who have high sedentism joining our ranks. Neutral have decreasing chance of joining. Low, accordingly, just want to go out.
Oh, of course, no 70-dwarfs waves, without reason!.. It might be better to make waves often, but certainly not in that numbers.
What's infusing our sedentism?
Permanent bonuses.
- "Last stand". Our brave starting 7 didn't get all this path along just to flee, like cowardly cobolds! Always have max sedentism.
- Immigrants have "+" to sedentism due their desire to live here. Disappears after time (after 1-2 weeks, see immigrants above).
- Noble idiocy. He wants to live HERE and nowhere else... Always max sedentism. Noble can change his mind and be apathetic (equals normal dwarf) or directed to leave your fortress (only caravans and expeditions, never has panic mood or use friend party).
- Specific reasons, like dwarf traveled towards another fortress, where hi/she want to live, ("-") or in other hand want to live here ("+").
- Ages of residence here. Only increasing with time. For example dwarf lived here ~10 years, may leave fortress only after some shocking accident (killed wife, massacre of all fortress...).
- Religion, cults, other worships of god, members of organization. All this give "+" depending on numbers (slowly increasing). Leaving any of them may give temporal "-".
- Something what dwarf like give "+" bonus. The same, destruction and disappearing of beloved object (and/or all of them) may give temporal "-". Artifacts also is in this category.
- Dwarf's victories. Killed titan, have engraving of own deeds, artifact, etc.
- Friends and family. They have serious influence on our poor dwarf, usually Urist get "+" from high "+"/0/"-" from neutral and "-" from low sedentism of folks. But this point might be very complicated due to relationships and personal treats.
- Casualties, deaths. This might take different effect due to personal traits, relationships and circumstances of death.
- Bad injuries. Have influence on family/friends. Might be "+" as well as "-" (for example, dwarf won't run on crunches to other fortress, because of fractured legs
- Fortress wealth. But with current mechanics it may cause some problems... I think wealth need to only shows current prosperity of fortress. Let's less dependence of created things (and wipe from goods, that is not on the map: traded, filched, destroyed), and increase - from working infrastructure (make it depend on statistics from last month, season, year, few years - in decreasing order). But it's another topic. Don't forget: wealth is divided between all dwarfs, and nobles want more % then simple labourer! How it works: basically, more dwarf skill/status - more wealth he wants (in absolute dwarfpoints). There might be dependence on traits too. According to this Urist gives +/-.
- Happiness. Might work as happiness statistic for last time.
Temporal reasons.
- War-like event. All courageous dwarfs give "+" ("We need to defend our fortress!"), but cowards give "-" ("I want to live in safer place").
- Out of supplies. No food/booze/water is more bad thing for fortress now. May cause massive emigration on the extreme edge of starvation/thirst. Immigrants take stare on your piles: they don't want either starve or thirst.
- No labour. Increasing "-" bonus in time. Smoothly diminishes when dwarf works. Don't stack while sleep, eat, drink, rest, out of mind. Don't work for migrant status.
Specific reasons.
Mayor is able to set immigration/emigration policy.
Immigration policy:
- "We don't need immigrants at all". Only "-". Override all others.
- "We need <number> of dwarfs of <profession> at least (not more, equal to) <number> level". If fit then "+".
- "We don't need <profession>". If fit then "-".
- "We need <number> of free hands (hauling)". According to labour levels and personal traits dwarf can accept ("+"/0/"-") or refuse.
- "We need <number> of free hands". Actually, it lets any job, but give no guarantee to dwarf about where precisely he will work. Only 0/"-". More experienced in one profession dwarfs get more "-".
- "We need <number> of soldiers". Similar to previous point. There may be split by military skills too.
- "Nobles? GO OUT OF HERE!!111!1" (on/off). May cause serious politics problems. But eliminates noble's immigration at all
Emigration policy.
In general it's not so policy about migration, but liberties and limitations.
- "Dwarfs (of <profession> at least (not more, equal to) <number> level, certain dwarf) give (at least, not more, equal to) (quality, quantity) bedroom/dining room/booze/food/breaks/etc". Sweet dream
To seduce legendary worker and evict idiots...
- "We want (<you>, dwarfs of <profession> (at last, not more, equal to) <number> level) to leave". Give serious "-" to sedetism. Might also be in form of forcing command (push out even if dwarf don't want to leave after getting minus). Exile command, you discussed above
Caravans and emigrants spread rumors about last seen protocol (both emigration and immigration), so it might influence your future migration sets (!)
Finally end... This is only basis, but what do you think about? Any constructive critics and suggestions are welcome.