The USGS maps used where published in the 1970s or earlier. Example: there is a 6 lane highway (990) here in Amhearst NY built in the late 1980s that is not on these maps. I have a Garmin GPS hand held that is 10 yrs old and the maps are more up to date and much more detailed. Im sure there are much better apps for hiking and out door activities.
Verklock about iHikeGPS : Classic Topo Maps, v5.2