Colonies and Outposts

RogerBW

The structure is tighter than the Commonwealth but looser than Empire. Colonies pay some taxes to the country that founded them, and are expected to trade primarily with it or its other colonies. Some of the older ones have become independent, amicably; it’s written into their constitutions that they may do so if enough of the population wants it and their economies are strong enough. (Some colonial powers are rather less liberal about defining “strong enough”.)
If a colonial resident wanted to move to and live in England, that would be no problem. If a few thousand all wanted to move at once, it might be a bit more sticky.
Life on a colony is slightly lower tech than on Earth, though it’s catching up, and you probably have to do an actual job, perhaps for as much as twenty hours a week. (How can they live like that?) Communication with other worlds is asynchronous (written, audio or video messages) rather than interactive, and the colonial sense of identity is fairly strong.
A colony is there because it’s a place that can support human life, and an initial group of at least 10,000 people could get together and afford (or get someone else to pay for) the shipping costs. Often that was a group with some strong sense of “us” about it, perhaps religious or ethnic; it may have drifted somewhat since its founding. Often there was something valuable there too which could be sold to pay back setup costs: rare minerals that could easily be extracted, odd biochemistry in the ecosystem leading to new drugs, etc.
There are also outposts, on worlds that are less pleasant to live on but have some other value, and in some cases on space stations. People don’t think of themselves as being “from” there: an outpost is somewhere you live for a few months or years while you’re doing a particular job, then move on. That’s not to say people can’t be born there, though it’s unusual; if you’re planning to have a family you probably move somewhere else first. Outposts include prisons, military bases, research stations, mining settlements, and so on.