TL;DR
Offline GPS apps use your phone's GPS chip (no cell signal needed) and locally stored maps to give you topographic navigation anywhere. Setup happens before the emergency: download the maps you need while on Wi-Fi. Gaia GPS is the best general-purpose option. CalTopo is free and covers the core functionality. Download your home area, your bug-out routes, and your bug-out destination at a minimum.
App Comparison
| App | Cost | Best For | Offline Maps | USGS Topo | Notes | |---|---|---|---|---|---| | Gaia GPS | Free + $20-40/yr premium | All-purpose backcountry | Yes | Yes (premium) | Best overall for preppers | | CalTopo | Free + $20-50/yr | Route planning, custom maps | Yes (mobile app) | Yes | Better desktop planning than mobile | | Avenza Maps | Free + paid maps | Specific official maps | Yes | Yes (downloaded separately) | Best for official agency maps | | onX Backcountry | $30/yr | Hunting, land ownership | Yes | Yes | Shows private vs. public land | | Maps.me | Free | General travel | Yes | No | Limited topo detail | | AllTrails | Free + $30/yr | Hiking trails | Yes (premium) | Limited | Not survival-focused | | OSMAnd | Free + paid layers | Open-source maps | Yes | Via layer integration | Steeper learning curve |
Gaia GPS: Setup for Offline Use
Gaia GPS is the most capable offline navigation app for emergency preparedness. Free version includes basic maps. Premium ($20-40/year, depending on plan) adds USGS topo, NatGeo topo, satellite imagery, and unlimited offline downloads.
Initial setup:
Key features to learn before emergency:
- Marking waypoints (long press on map, or use the + button)
- Recording a track (shows where you've been)
- Importing and viewing GPX files
- Checking coordinate display format (set to MGRS/USNG for compatibility with paper maps)
Battery management: GPS is battery-intensive. Enable battery-saver mode (Settings > GPS Update Frequency > Every 10 seconds or Every 30 seconds instead of continuous). Carry a battery pack rated for at least 20,000 mAh for extended field use.
CalTopo: Free Alternative
CalTopo.com is a web-based planning tool with a companion mobile app. The desktop site is excellent for printing custom maps at any scale. The mobile app provides offline navigation.
Offline setup (mobile app):
- Plan your area on caltopo.com on a computer first
- Download the CalTopo mobile app
- Create a CalTopo account (free)
- In the app, search for your area
- Tap the download button to cache the current map view
- Navigate to your area, zoom to the detail level you want, and download
- Offline maps expire after a period — re-download before any emergency
Custom map printing from CalTopo: CalTopo lets you create precisely scaled, custom-area maps combining USGS topo, satellite imagery, or any other layer, and print them at any scale. A 24x36-inch custom map of your local area at 1:24,000 scale is printable for a few dollars at a print shop. This is the best approach for creating printed backup maps.
Avenza Maps: PDF-Based Navigation
Avenza Maps takes any geo-referenced PDF and provides GPS navigation on that map. The key use case: official agency maps (USFS motor vehicle use maps, BLM surface management maps, state park maps) that are published as geo-referenced PDFs.
Setup:
- Download Avenza Maps
- Find your desired map through the Avenza Map Store (many are free, especially government maps) or download geo-referenced PDFs directly from agency websites
- Import the PDF into Avenza
- The app overlays your GPS position on the static PDF
The USFS publishes motor vehicle use maps (MVUMs) for every national forest in geo-referenced PDF format, available free at www.fs.usda.gov. These show road and trail access information that topographic maps don't include. Downloading these for your region adds important detail to your navigation kit.
Download Priority List
Download before any emergency:
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Home area: 50-mile radius, all zoom levels 10-16. This covers evacuation routes from your home.
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Bug-out route corridor: 20 miles on either side of your primary and secondary bug-out routes from home to destination.
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Bug-out destination: 20-mile radius around wherever you're going.
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Regional map: Your state or region at lower zoom levels (8-10) for general orientation.
Storage budget:
- Home area topo: ~200 MB
- Route corridors: ~300 MB
- Destination area: ~150 MB
- Regional overview: ~50 MB
- Total: ~700 MB for comprehensive offline coverage
Most modern phones have 64-256 GB of storage. 700 MB is entirely manageable.
Keeping Downloads Current
Set a calendar reminder to update your offline downloads every 3-6 months. Map data is updated periodically. An offline cache from 2 years ago may be missing new roads, changed trails, or updated facility information.
USGS topographic data changes slowly (terrain doesn't change much). Satellite imagery updates more frequently. Routes and roads change occasionally. Keep topo downloads current at minimum.
Sources
Frequently Asked Questions
Do these apps work without cell service?
Yes, when you pre-download the maps. GPS location requires only the GPS chip in your phone — no cell signal needed. But maps require a data connection to load unless downloaded in advance. The critical step: download the maps you need while you have Wi-Fi, before any emergency. All apps listed here support offline map caching.
Which app is best for survival/prepper use?
Gaia GPS is the most complete option: USGS topographic layers, satellite imagery, offline downloads, GPS track recording, and waypoint marking. It's $20-40/year for premium features. For free: CalTopo's mobile app has strong topo functionality. Avenza Maps is best if you have specific PDF maps you want to geo-reference (like USFS motor vehicle use maps or specialized sheets).
How much storage do offline maps require?
USGS topo coverage for a 50-mile radius around your home: approximately 200-500 MB depending on the zoom levels downloaded. Satellite imagery is much larger — expect 1-2 GB for the same area at usable zoom levels. Download topo maps as your baseline; satellite imagery as supplemental if storage allows.