OK this is a subject i am VERy into// and i feel like Glacier folks do a lot off trail and route finding hikes that benefit from advanced GPS use, so i'll go into detail here..
i cant resist posting some basic info, people already using their phone as a GPS might skip the "BASIC" and "Phone vs GPS UNIT" sections and skip down to "GPS APPS"...
Phone vs GPS UNIT : the BIG questions are do you just need to find yourself on the map from time to time?, or do you want to track your hike?, And for how long? if you want to track your hike so that you can later upload a .gpx or similar file to your computer or CalTopo, or if you are bushwhacking and absolutely need to recall the same route, a high end handheld is best especially if you are under heavy tree cover and out for days mainly because those units have much longer battery life and lose signal less often. The main advantage of handhelds is they take AA batteries and last a long time, but with many people carrying a battery pack and a solar panel that is a non issue.
Some other advantages of a decent handheld gps are they are more durable, have other features, and that it may come with preloaded maps. They are often not of the best detail but depending what unit ($$$) you get they can be good, and will be simpler than adding maps to your phone... but from what i have seen, it is worth the effort to add good maps to your phone.
Overall very few actually need a handheld gps. If you can afford a high end unit, they are a great extra device to have, but probably overkill for most.
BASIC... Better phones have better gps units, but i have found even the iphone 4 was decent, and at least as accurate as my low end garmin. - a better garmin etc will be a few feet more accurate, the batteries will last longer. Garmin type will work better under heavy tree cover- only IF you get a higher end unit.. otherwise, the average 2015 or newer phone GPS is more than accurate enough. Phones work better than my 2003 etrex.
You need "location" turned on but if you turn off wifi and use airplane mode, the battery will last longer.
Best to carry a spare battery pack and/or solar panel, especially if you want to track your route.
Tracking your route uses far more battery, but may be essential for a bushwhack.. ill say it a few times, carry a battery pack..
A problem i discovered (the hard way, at night/ ugh)- if you let the battery get too low the gps may update your position less frequently, or not at all, and can throw you off. (easily avoided by carrying a battery pack, but they are not exactly light. 10 000 mAh battery pack, about 4 phone recharges is about twice as heavy as a phone).
I won't get into the camera aspect other than to say the newest high end phones have much better cameras than a few years ago, are pretty good for non-zoom video, and it's a good option for people who would otherwise either not carry a camera, But- If you like to use manual settings and a tripod, phones are not there yet.
GPS APPS-
What throws some people off is some areas especially back east have cell service even in the woods so people are using the maps without downloading. In the West that will not likely work. No service, no internet, no map. All you really need in terms of an app is one that allows you to download maps to your phone. There are many gps apps that do this, if you find one and like it , it is probably good enough...
All apps require you to add/ download maps for offline use, most work in a similar pain in the neck fashion.. online, you zoom in on a map, press one corner of the area you want, drag your finger to make a rectangle around the area you want to download. Then select zoom level and Cache/ download/add the map to your phone. i'll discuss zoom level a little more below.
GAIA (and some general app info)-Gaia Is "the" gps app. The stuff that comes with the premium membership... seems like a lot of extra junk most wouldn't need... Free GAIA only allows you to use One type of map for free, and ONLY online- that is while you have cell or wifi service... paying for the regular membership is necessary to make the app useful. If i'm reading this right you could theoretically get all the maps you needed, then stop your membership. Can't say for sure, they may rescind your downloaded maps if you cancel your membership. VERY annoying as that raises their price exponentially... it used to be $20 to buy the App, get free map downloads, and the subscription was for additional services. Not anymore.
Route planning is the main reason for the advanced apps, which seems unecessary for most hikers.. we know what trail we want to take from a to b, we know the mileage.. we just need to locate ourselves on a map ..
unless the hike has never been done before, there is probably a gps track you can download and use for distance and elevation data if you really want it from a site like Caltopo for free... Gaia and Alltrails services want you to subscribe to get access to the "trips".
Elevation profiles and other details are nice to have, and sometimes the "trip" features can give you miles to go or other useful details. People thru hiking lnger trails often use GutHook which includes water sources, good campsites, a lot of extra info along particular trails.
I could go on for a long time about the complexities of adding routes to maps and why gps apps can't calculate mileage or elevation profiles in advance, but put simply the App Subscriptions are primarily about getting the ability to plot your route in detail and then watch yourself follow it on the screen with miles to go indications. If you do the same hike twice, you could track it the first time and create your own "trip" file for next time.. If you want to know more about adding .gpx files ask and ill try to help..
When you get a cheaper app without a subscription, you get just about everything else for a lot less money. You just end up having to do a litle math in your head sometimes, read the scale of miles and contours, and calculate roughly.
I'm a fan of Cheap so i went with US Topo Maps ($10) which is for android only, sorry i don't have an exact better suggestion for Iphone BUT - both the other apps mentioned, iHike and Topo+, look good and have what you need most- the ability to download maps, and different types of map to your phone. Should be obvious but not everyone realizes, you need to download the map and store it on your phone or else it wont't be there when you are out of range. It is worth it to spend a few bucks and not deal with ads or other restrictions.
If you want to use an Iphone, get one with a good size memory// advantage Samsung, dropping in a microSD is easy. Depending on how many areas you hike in, the maps might take up a lot of space after awhile. Glacier Park in it's entirety must be around a gig in a good zoom level.
Which map should you download??
USGS or proprietary maps like "gaia topo" are extremely detailed but often take up huge amounts of space.. if you are only going to use a map once you can of course delete it later but if you plan to store many maps on your phone, you might not want the biggest files..
I have found OpenCycleMap (oddly, the bicycle map) has had every trail, every crazy tiny 4wd dirt road, very good contours and the maps are far smaller than other options with as much detail.
There are a Lot of choices in the "map layers" section of your app, check it out and play around with different maps, see what you like best...
Caution- if you download maps of different types, you will need to switch "map layers" to see them. You may find yourself saying "i know i downloaded this map, why is my screen blank".. check the layers setting...
Detail Level/ Zoom level- note this setting when you download maps. i still haven't got it for certain but seems like level 14 maybe 16 at most is more than adequate. Level 18 results in HUGE files with zoom farther in than is useful. I also like having a low level zoom of the entire region for reference. Level 12 is a very useful intermediate zoom.
Some of this was probably confusing and i can try to clarify anything people might wonder about but i hope this helped people figure out how to get the most out of their phone gps.
I strongly suggest a compass, and either knowing the trails or having a paper map as well as using landmarks to track your progress but gps sure is a lot of fun to work with....
A little more if you want to get extra nuts with the topo maps... many of you may be aware, but just in case - the USGS store allows you to download a large array of topo maps of every area they have maps for, for free.. different scales, different years. You could print these maps out for backups, or...while the only software i have found that gps enables PDFs on a tablet or phone is a very expensive app by Terrago- "Terrago Toolbar" is a free plug in for adobeReader (laptop, pc/mac only) that GPS enables your USGS topo maps on a computer. Not great for hiking, but not a bad way to have extra detailed gps maps in your car if you have a laptop and a gps usb unit (i had bought microsoft streets and trips, a roadmap for PC which came with a usb stick gps)... The newest maps are not great, too many layers too large files.. extra info that might be useful to some, but 2000 or earlier topo maps are more like what most of us would be familiar with. Because sites change their exact names occasionally i recommend searching "terrago" or "usgs store" to find these products. Probably not much use anymore with so many detailed maps online these days, but if you want to download the originals, USGS store is a great site.
well that's probably more than too much but hopefully someone finds some of this useful...