Hiking in Japan is predominantly along well marked trails and paths, however it is not wise to up these mountains without a map or GPS especially in the harsher seasons or if you cannot read Japanese or Kanji (here is a great site explaining some useful Kanji and map features). Make sure you are prepared when you hike!
Free Printable Topographic Maps of Japan
If you’re looking for free printable topographic maps “地形図” of Japan the Japanese GSI have an online map that you can print from. The website is in Japanese but have a look at the image below to see how to do it. You can print to A3 or A4.
Learn how to read a topographic map
While many people hike using GPS devices it is highly recommended to make yourself familiar with a topographic map of the area you are hiking in. There are many sites on the internet where you can learn how to read and use a topographic map and compass. Like this one.
Even thought I have GPS available I always carry a compass and a paper copy of a topographic map with me! This is a good site with a lot of information about topographic maps and navigation in Japan.
Useful Navigation Apps
I use two different navigation apps when I am hiking in Japan and both are free on Android. First, I use the Android WikiLoc app to record my hikes as I go and then I upload the trails to the WikiLoc website afterwards. This allows me to see how long the hike took me exactly, and record where I went. From the WikiLoc website you can download the .gpx files of over 5,000,000 hikes, walks and bike trails from around the world.
Second, I use the GPX Viewer android app while hiking to keep an eye on my progress and occasionally check to confirm that I am going the right way. While most of Japan’s mountains trails marked; if you can’t read Kanji, if the signs are old or inaccurate of if there is low visibility it helps to have some way to check your position. I load a GPX file of my route before I leave, select a topographic map and let it load on the app and then turn my phone on to airplane mode to save battery on my hike. This system seems to work well for me however if you’re doing more serious or risky hiking you should consider investing in a proper GPS device.