Both present continuous and be going to can be used to express the same idea. In some cases there is a difference of meaning.
The present continuous is mostly used to talk about fixed arrangements. Be going to is mostly used to talk about intentions.
- I am going to get a new job. (= I intend to get a job.)
- I am getting a new job. (= It is already decided / arranged.)
- What are you doing this evening? (A question about arrangements)
- Are you going to do anything about that letter you received from the civic authorities? (A question about the intentions of the listener)
- I am seeing Peter tomorrow. (Here the emphasis is on the arrangement that already exists.)
- I am going to ask him to stop borrowing my car. (Here the emphasis is on the intentions of the speaker.)
Events outside people’s control
We do not normally use the present continuous to talk about events that are outside people’s control.
- It is going to snow before long. (NOT It is snowing before long.)
- Look at the sky. It is going to rain. (NOT It is raining.)