The present continuous used for the future implies planning and arrangement:
There is a suggestion that more than one person is aware of the event,
and that some preparation has already happened. e.g.
I'm meeting Joe at the station > implies > Joe and I have arranged it.
I am arriving tomorrow. > implies > I have my ticket.
We're having a staff meeting next Monday. > implies > The staff knows about it.
Another instructor adds intention as an implication, and wisely recommends mentioning the future time frame to avoid ambiguity:
We use the present continuous tense to talk about the future when an
action or situation is part of a (sic):
Mary’s studying in the library. (now)
She’s studying at Bethan’s house this evening. (future)
The notion of near future will be impacted by the intensity of the intention, planning and arrangements.
- We are meeting next week.
- He is graduating next May.
- I am retiring in six years!