You'll find quite a few apps available for Yosemite and some look good on the surface. However, most of them rely on your mobile device having a strong enough connection that you can access the data you need to make them work. Unfortunately, many parts of Yosemite have little or no signal, no matter what carrier you use. That makes it likely your app will simply refuse to work when you want it to. As of May, 2013, when we last evaluated Yosemite apps, there's only one app available that avoids that problem.
Chimani App for YosemiteIf you like to use apps to plan or assist during your trip, there’s a free app that provides a lot of information about Yosemite, created by Chimani, who make apps for many of the big national parks.
Its strength is that it’s self-contained, downloading a lot of data to your mobile device – which is the most reliable way to handle it for a place like Yosemite, where mobile phone signals can be weak or non-existent. The downside is that it makes the app large (so large that you need a WiFi connection just to download it) and in total it added 1.1 GB of data to my iPhone.
You’ll find a lot of information in the Chimani app, with 34 icons on four screens at the top level. Some parts are more useful for advance planning than use in the park, but unfortunately they're mixed with sections better used in-park and navigating the app may be harder than finding your way around on the ground. Some icons are also hard to decipher.
If you really like to use an app while traveling, Chimani has a lot of offer and is the best Yosemite app currently available, but if you’re good enough with a map to figure out where you are, you may find the old-fashioned paper map you get at the entrance an easier choice. And if you want to go hiking, Chimani is not designed as a serious trail-finding tool.