DIFFERENCES BETWEEN THE PRESENT CONTINUOUS AND THE GOING TO FUTURE
The Present Continuous is used to describe an event in the future which has already been arranged by the time of speaking.
e.g. They are visiting the Prado Museum next week.
=(They’ve got the tickets)
Compare this with the use of be going to:
e.g. They are going to visit a museum sometime next week.
=(The visit is not arranged yet, the focus is on their intention)
We usually use the Present Continuous for future events which involve other people and where we have made some form of commitment (eg. buying the tickets). However we can also use this tense for arrangements that don’t involve other people. In this case we see it as an “arrangement” the speaker makes him/herself.
e.g. I’m staying in tonight. I’ve got lots of paperwork to do.
The focus here is on the “arrangement”, i.e. there is no suggestion that the speaker wants to stay in, which is the case when we use “be going to”. Compare:
e.g. I’m going to stay in tonight. (focus on intention)
We also use the Present Continuous for impersonal plans:
e.g. Computer City has announced that it is opening four new shops next month.
We cannot use this tense with events which are beyond human control, e.g. the weather, because these events are predictions, not intentions or arrangements.
e.g. It’s going to rain tomorrow (not It’s raining tomorrow).(From Advanced Learner’s Grammar- Longman-)