iOS apps for viewing generic map files What are the iOS map-viewing apps that are compatible with the largest number of file formats for topographic maps and trail maps? (such as those found on the USGS website)

I'm really looking for a no-bells-and-whistles mapping "swiss army knife" app that's LOW on branding and not trying to sell me maps.
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.