Lesson Plan 8 - Where am I?

I would like some clarification on these three similar words, please En haut = At the top Par dessus = On top of Sur = On/Over Are the words 'par dessus' and 'sur' interchangeable ? Can they be used in the same situation. For example, could one say Le chat est par dessus le paillasson. .... or Le chat est sur le paillasson. Also, when using the term 'en haut' is this phrase used for sentences such as, I am at the top of the class. Je suis en haut de la classe.

After I made the first post, I had an additional question about lesson plan 8. I would like to know if there may be a typo in the answer key, for question 22 and 23. I'm not sure how to do accents in the forum, but my question is not regarding accents, I think there might be a word or two missing from the answer. The answer for question 22 is "L'ecole est vis a vis de l'eglise." The answer for question 23 is "L'cafe est vis a de l'ecole" Should #23 be "L'cafe est vis a vis de l'ecole"???