I've decided to hike the Appalachian Trail this summer, and one of the items I'll be taking to aid me in my trip is my 16GB Retina iPad Mini (aka, iPad Mini 2). The decision to take the iPad was rather easy for me, especially considering the paper guidebook I am taking (now, as a PDF) weighs nearly 2/3 the weight of the iPad. Add the weight of my Bible and one additional book or journal to that and we're already over the weight of the iPad.
Plus, I'm a geek, and a technophile to boot. So of course I'd prefer to do all of my planning, mapping, and reconnaissance prior to the next day's travels not hunkered over a paper map and red lens flashlight underneath a poncho in the rain as I did in the Marines, but kicked back against my pack with an iPad, under the stars (maybe under a poncho, weather depending).
That being said, I'm using my iPad for numerous purposes along the trail. This particular post will be how I've managed to get a very particular peg, into a very particular hole - the downloading of Google's phenomenal terrain maps into the MotionX GPS app for iOS.
First, and the most tricky part, is that most applications do not license Google's terrain maps for offline use. My personal assumptions are because it's a) probably pretty expensive, and b) because most people don't know how to read, or have much use for, detailed topographic maps.
The MotionX GPS app has many built-in maps, but only three of which are available for offline use (MotionX Road, MotionX Terrain, and NOAA Marine), and they're not up to snuff for what I need. What the app does provide for is custom maps - this is our inroad for downloading the topographic data from Google.
After much Googling, I stumbled across a very detailed how-to on a Land Cruiser forum (of all places) for various URL schemes for many mapping services across the net. So they don't get lost to the ether, I've included them at the bottom of this post, along with the Google terrain url scheme immediately below (that works at the time of this post's writing):
MotionX provides instructions in-app, but the gist is that as you scroll around a map, zooming in and out, the app will dynamically fill coordinates into the [X] and [Y] of the URL, while substituting the zoom level for [Z]. Each mapping site has it's own custom url schemes, which you will have to determine for yourself.
After that, the MotionX App provides a relatively seamless interface for determining what levels of zoom you would like to download, whether you'd like an area download (a circle) or a route (an oblong circle), and how much space on the device the download will consume.
One plus the app has going for it is that it will not download duplicate tiles, so if you overlap your route with another section, you don't have to worry about getting duplicate tile downloads or wasting space on your device. Additionally, and more importantly, you can set the minimum and maximum zoom levels downloaded to your device to further minimize the download sizes.
I found that while I wanted to save as much space as possible (again, I'm using an older iPad that's only 16GB), I didn't have to zoom too far in or get too nitty gritty with how close to the trail/route I was working. As you can see, the map segments aren't too large and shouldn't pose much of a storage issue for most.
Map Source Examples
USGS Base Maps
Open Street Map (OSM) Terrain
Aerial / Satellite