This rating is originally made for hiking in Taiwan but it may also partially applicable to hiking (tramping) in New Zealand as the basics of hiking are universal. The difficulty rating of the hiking trails is only based on my subjective opinion and the rating for each trail on this website is just the impression from my limited experience.
This rating is mainly for a solo hiker who wishes to manage all matters of hiking without the assistance from anyone in the mountains. (If this hiker joins a guided hike or hire a mountain assistant, the difficulty rating of this particular trail may be reduced.)
This difficulty rating is only for the hiking activity which people follow an existing trail, not including any other possible outdoor activities around this trail such as off-trail hiking, rock climbing, ice / snow climbing, water sports, air sports…etc.
The transportation to arrive the trail heads is not a part of the rating. The possible weather condition is not a part of the rating either. But hikers must be aware that the bad weather including the presence of snow and ice increases the difficulty of hiking substantially and by staying in the mountains for a longer period of time the hiker is more likely to be exposed to any bad weather.
★☆☆☆☆ Easiest: This very popular trail is suitable for all levels of fitness, but people with mobility issues may find it is not safe in some places. The trail is well-formed, marked and maintained frequently. There may be gentle gradient along the trail or some stairs. A few spots may be exposed but not result in considerable safety concern. Hikers can return to trail heads within several hours.
★★☆☆☆ Easy: This popular trail is suitable for hikers with average fitness and know the basics of hiking safety. The trail is well-formed, marked and maintained frequently but can be muddy or slippery. There are one or more steep sections along the trail. Scrambling may be required at some spots.
★★★☆☆ Advanced: This trail is for experienced hikers who have a basic level of navigation and route-finding skill and know how to stay safe in the mountains. A hiker who is at or above this level should be competent to multi-day hike. The trail is obvious to follow and marked but one or more sections of the trail may be steep and exposed or prone to damages by severe weather. Elevation gain in one day can be up to approximately 1000m.
★★★★☆ Difficult: This trail is for experienced and fit hikers who are familiar with all of the essential hiking skills and have in-depth understanding of the topics mentioned in “Hiking Safety in Taiwan.” The trail may be steep, faint, overgrown or very exposed. Trail markers are not regularly maintained and sometimes it may be hard to find. Total self-sufficiency is required to hike on this trail.
★★★★★ Very difficult: This trails is for experienced and very fit hikers who have done multi-day hikes with self-sufficient manner for many times. Hikers of this level should master all the skills and knowledge mentioned in the “Hiking Safety in Taiwan.” The trail can be very steep and exposed; sometimes become difficult to follow because it is faint, overgrown, damaged or lack of markers. Trail markers may appear intermittently or are only present at the locations where necessary. There may be no shelters along the whole trail.