Offline Maps on Mobile Devices
Offline maps can be a useful tool when mobile network coverage is unavailable. Two of the most common file formats are geo-referenced PDF and geo-TIFF files. These formats contain a map image and also the necessary geolocation data to render your position on these maps. With the right geo-referenced file it’s possible to navigate without any dependency on a network connection, although a GPS/GNSS signal is required for a compatible app to locate your position on a map.
Another thing to keep in mind with these offline maps is to plan ahead. Download and test these maps before reaching your remote destination since a network connection is required to download the maps.
USGS has an online tool for selecting an area within their coverage area and exporting to PDF format. Note that their download process is asynchronous so they will send a followup email when your requested map is ready for download.
Where to find geo-referenced maps
The FAA produces many geo-referenced maps for pilots.
One thing to note is that FAA sectional charts can be of large file size so it may make sense to use a tool such as QGIS to select a portion of a larger map or to resize to a smaller file size when using on a memory limited device.
BLM has maps for campgrounds, recreation areas and other public land.
CalTopo.com is another popular option with a free tier to generate custom maps.
Allmaps is a great resource, especially for information on finding and using historical maps.
Make your own for free
You can make your own geo-referenced maps for free using tools such as QGIS. With QGIS it’s possible to use OpenStreetMap, OpenTopoMap, Google Maps and many more. QGIS is a powerful tool available for Windows, Mac and Linux.
How to view offline maps on mobile devices
Gaia GPS is a popular app with versions for both Android and iOS.
Avenza Maps has apps and also a large library of maps to download within their ecosystem. Note that many of their maps are available for purchase only although some are also available at no cost.
Inveo Maps is a newer entrant with a simple user interface for viewing geo maps on iOS.