as above

but i am assuming that your square map is in Mercator projection from 85 north to 85 south

this will need re-projecting to 90 north to 90 south and in equirectangular simple cylindrical format
see:
https://en.wikipedia.org/wiki/List_of_map_projections


from this
https://en.wikipedia.org/wiki/Mercator_projection
to this
https://en.wikipedia.org/wiki/Equire...lar_projection