iOS apps for viewing generic map files
It looks like Maps n Trax could help:


  With [it] you can view your own maps on your own iPhone instead of
  just generic online maps or a limited selection of maps chosen by
  somebody else. […] for specialist maps with details that are not
  available on other mapping applications, such as highly detailed
  topographic maps […].


From the description, this looks like something you could use. An user guide can be found here. NB: im am not affiliated with them.