Thread: GPS Advice
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Old 04-25-2017, 09:53 AM   #18
Trail Boss
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Join Date: Nov 2010
Posts: 902
When it comes to maps, almost all backcountry navigation apps work the same way.

When connected to the Internet, you can display and browse online maps like USGS Topo, TF Outdoors, etc. These are "raster maps" which means it's like looking at a JPG or PNG image (the map is built of small square "tiles").

When disconnected from the Internet, you can't display any of those maps.

Some apps can "cache" portions of a map (keep a copy in the phone's local storage). In other words, while browsing a map online, they keep a local copy of whatever you're looking at so later, when you're not online, it can show you the "cached" portions of the map. However, it can't show you anything you didn't look at when online, nor can it display the cached map at another magnification level (unless it was also cached when online).

While you're online and browsing a map, you can define an area you want to keep on the phone and instruct the app to "go get it". You also tell the app how many magnification levels you want (the highly-magnified levels contain more detail and take more space) and then it downloads it to your phone. Now you can use the downloaded map offline. Because these are raster maps, they aren't very space-efficient (each magnification level is a separate map). It will only contain whatever area you originally specified and only the magnification levels you requested.

Locus Map (and a few other navigation apps) convert OpenStreetMap data into "vector maps". Each vector map typically contains an entire country, state, or province. It can be viewed at any magnification level. It also contains searchable Points of Interest (search for "Lake Placid" and it will pan the map to the town). It can also contain a Digital Elevation Model (DEM) which means it knows the elevation of every point on the map (this is not the same as contour lines). It is also far more space-efficient than a raster map. The entire state of New York fits into less than 300 Mb. Locus Maps calls these maps "LoMaps" and gives you 3 free LoMaps. Within Locus Map, there's a link to the Locus Store where you can download your first three free maps. Afterwards, the maps cost a few cents per state. OpenAndroMaps is another source of (free) vector maps but stick with LoMaps for now.

I recently did extensive OSM work on the streams and trails located on AMR property (including Cathedral Rocks and Bear Run). I don't usually post my Changesets on ADKhighpeaks until a few days after I've done the work because it takes several days for the changes to "percolate" to all magnification levels.

I should caution you that the mods I made to the West and East River trails as well Cathedral Rocks, etc are based on skimpy data I sourced from Strava's Heat Map. I also referred to the DEC "Roads and Trails" data but it was demonstrably inferior (its highly simplified trails disagreed with data collected from multiple GPS tracks). I added "Fixme" tags to the trails (only visible to map editors) to ensure the next person knows these trails need to be refined.
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