MAPS THAT LET YOU CREATE, EDIT, AND SAVE GPS FILES
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A full featured program or app should have all the editing tools necessary to create and fully modify GPX tracks and waypoints. It should also be be able to export and import GPX files, have at least one high resolution topographic map, one terrain and road map and one map of good satellite imagery. It should also be able to download maps for offline use. 
The most popular and best on the internet, and on an android app. ​Create and edit tracks, upload, download, and organize GPX files, and print 5 maps for free. A $20 subscription gives you twenty max size 13X19" PDF maps, and $50 gives you fifty max size 36X48" maps.​
Primarily a mountain bike site, this application has the potential to be the best map resource for trail planners. This strength comes from the detailed trail specifications, trail reports and other features.

FATMAPS
Fatmaps is a 3D map viewer. 
​For $30 a year onXmaps shows who owns private and public land anywhere in Idaho (or other states). ​Their motto is "Know where you stand."

Idaho Hunt Planner
Upload or create a route and print a map but not download GPX.

Windows software.  Edit GPS data faster than the internet apps. Plus there are a few tools that other apps don't have for working with large gpx files.

Georeferenced PDF maps are selected online and downloaded to your phone. Some are free. Many are not. This app is popular with government land managers. 
Wikiloc  Video and Pictures can be added, a driving map to the trailhead can be created, and a GPX trail map file can be downloaded. It also has iPhone and Android Apps.
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All of these map pages are produced by Recreational Equipment, Inc., commonly known as REI, is an American retail and outdoor recreation services corporation. ​