Mountain up north on small maps (5)
I believe the answer is:
plans
'maps' is the definition.
(I've seen this in another clue)
'mountain up north on small' is the wordplay.
'mountain' becomes 'alp' (the Alps are a mountain range).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'north' becomes 'N' (abbreviation).
'on' says to put letters next to each other.
'small' becomes 's' (abbreviation - e.g. clothes size).
'alp' written backwards gives 'pla'.
'pla'+'n'+'s'='PLANS'
(Other definitions for plans that I've seen before include "Schemes; diagrams" , "Aims" , "Stratagems" , "Detailed proposals for doing something" , "Intentions or drawings" .)