Thought I'd post separately on another app I like that I don't think has been mentioned, Gaia GPS. This is another example of an app I got early on, and it's been steadily improving and adding features. For Android and iOS.
It's similar to the Trimble apps in that you can start with a base map and then add overlays. Where it kicks over Trimble, Avenza or Motion X or others is in the selection of maps. It basically allows connection to any "TMS tileserver," or tons of online resources for mapping.
There's OpenStreetMap (several flavors), Google maps and views, New Zealand topos, Canada topos, CalTopo (an awesome resource; worth checking out
www.caltopo.com), USFS visitor (the big old ones you buy, NOT the topo ones!), etc etc. I mean you can overlay 1930 topos if you want, maybe not trivial if you're a ghost town fan).
Let me emphasize: you can use USFS and NPS visitor maps, and they're georeferenced! So you can say open one of those nice little maps Death Valley rangers give you and drop a waypoint on it. Sweeet. It also has a great collection of POIs. E.g., on the DVNP map I mentioned it had one for Pyramid Pk; click on it and it takes you to
www.summitpost.com to find the way up. Or the Chicken Ranch (it takes you to wikipedia for that one
. The POIs show up in categorized list, so you can just go to say "campgrounds" and then tap them to get directions. And these directions take you right to Apple's nav app, so you have turn-by-turn from wherever. Or it will guide you within the app, if you're going crosscountry or hiking.
Like Motion X, you can select certain tiles to download for off line use. In my experience, it's also one of the fastest at rendering maps.
If you a map geek, this is for you. It has syncing (to their own cloud source) for sharing, as between tablet and phone, e.g. And you can email a gps track using a certain string in the subject and it will import it. They even have a website where you can attempt to modify your own maps for use in Gaia GPS. And they have a "download maps along track" feature that really makes it easy to download what you need.
I'm not particularly fond of their navigation along a route screen; it shows the map along with direction, distance, etc. I like the compass views in some other apps better, but having the map right there is nice in certain situations. And I like the recording feature, which I more often use than the "guide me" to feature.
Like Trimble, they also have a premium subscription service. The selling point is the ability to customize map layers. In the regular app you have the choice of many layers, but only one at a time. With the premium service, you can have several, say satellite and Nat'l Park Map. And you can adjust the transparency of each. You can do this offline and then download your custom map to your phone.
I haven't investigated all the iOS apps out there, but this one definitely seems to the best in terms of map coverage. Better than even Avenza's. And they have great tech support. At $20 I found it the best out there; worth it just for the USFS maps.
Rob
PS: I added a CO Motor Vehicle Use Map by downloading a tif and rectifying it with Gaia GPS's open source website,
http://warper.gaiagps.com. You can go to the link below and see the map overlaid on OpenStreetMap, and adjust the transparency (hit the "preview" tab). I then used the site's ability to create a gaia URL which I emailed to myself, and then opened it in Mail on my iPhone, clicked it, and it imported this map into Gaia GPS. Pretty easy.
See the map here:
http://warper.gaiagps.com/maps/494