simple present used for future context?

Question

In writing exercise "A perfect day in Granada", I am expected to use simple present tense to talk about the near future plans. And the "ir + verb" structure is not accepted as an alternative correct answer. Why?

Answer

Because the test said 'In this exercise you'll practise El Presente. The future can also be expressed using the present tense. This tends to be used for something which will happen soon.

Using Ir + a is not wrong but it was not being tested in the exercise.

Answer

Hola Shafagh
While you went through the writing challenge you will have found "Lit:..." notes for those sentences using the present tense instead of any future form. This indicates that you need to write the sentence as it would be "literally". 
Here is our lesson on:
Using El Presente for future actions
Saludos
Inma