It sounds like the institution you are applying to is trying to see what your goals are for your education as well as your future in order to properly align you with an area of study that will benefit you the most. For instance, if you want to do environmental research, they want to make sure you get in a program that will be of the most use for you.
You need to discuss your research interest here. What do you want to research? Why? How do you intend on using your data? What are your plans in this field? All of these things are important to include in this type of essay.
I hope this helps you get started.