Bivouac.com   Discussion Page   Home     Help   Index     Login
Background Maps For Your GPS
Back To Discussion List
ArticleId: 4844 Written: 2017.05.05 by: Robin Tivy

As you know, all modern GPS units and smart phone GPS Apps have background topo maps. I call them "background maps" to distinguish between them and "overlay" data such as trails and roads from Bivouac. The overlay data is typically stored on the GPS as "track logs" and "waypoints". The background map provides the contour lines, streams and art work. This discussion is about the different options for those background maps.

Vector versus Raster
On a Garmin GPS, the background maps are a "vector" format, and often built in. Vectors are much more compact than the original "raster" scanned images. So it is possible to put maps for all Canada on your GPS. But the vector versions lose some information, and do not contain background colors, tree cover, etc.

On smart phones, the typical Apps I'm talking about use raster maps. The scanned image is broken up into little "tiles". As you pan around the map, the App asks for the necessary background tiles from a "tile server". The advantage of the raster "tiles" is that they can contain all the original art work and coloring of the original map. But they take more space. As long as you are connected to wi-fi, the extra space requirement is not a disadvantage. The phone can simply request the necessary "tiles" as you pan the map. The only tiles it needs are the ones that correspond to what you are seeing right now on the screen.

Caching
However, once you are in the backcountry, the tiles are no longer available via wi-fi or cell coverage. They must be stored in the memory of your phone. Thus the apps all have a mechanism whereby you download the maps you will need in advance and "cache" them on your phone. Typically the original idea was to just download the maps you needed for any given trip. The download function allows you to zoom out and draw a rectangle on your screen of what maps you want, and then cache them. The typical rectangle might be 30 km by 40 km. Depending on the maximum memory you allow the app to use, when you do the next trip, the app might bump out the oldest previous maps.

On my Samsung phone, with 16 GB of memory and an extra SD card, I have downloaded all the the maps for an area about 150 x 150 km square. (From Vancouver to Pemberton or Manning Park. Once I go out of that area, then I have to download the necessary maps. For example, on our trip to the Kootenays, we'd drop into a wi-fi coffee shop just before setting out, and download the maps.

Now that you know the theory, you can see the Standard GPS Operations table, and find out exactly how to download maps for your given App.

Choosing different background maps
One advantage of the smart phone apps is you can choose what maps you want, and they are typically free. On the Garmin, you typically have only Topo Canada. But on the smart phone, there are three or four great background map series that you have available in BC and Alberta. And then you can download maps in any other part of the world as well.

Where do these maps come from? For most provinces except BC, the only REAL sources of contour data are the contours on the NTS 1:50,000 maps. That series took at least 30 years for the geological survey of Canada to complete. So you aren't likely to suddenly see all sorts of new map data. The arial photos they took were accurate enough to draw accurate 100 foot contours on a 1:50,000 scale map. Although you may see digital maps that appear to have more detailed contours, don't be fooled. They are just interpolated from the same basic data.

In British Columbia, there is one other source of accurate contours, and that is the TRIM data. It is accurate enough to support 20 meter contours. In my experience, they are often more accurate than the old 100 foot contours, but not always.

It is worth mentioning that there may exist small pockets of more accurate contour data, such as for mining projects or forestry, but this data is not organized into a systematic map series of any sort. None of this is available on GPS.

Other series of paper maps exist, such as listed in this table List of Paper Map Series.

Names of Data sets
To discuss the names of the different background map series, the best thing is to start by looking at them on Bivouac GMap. Go to any mountain page, and click "GMap". The default is the NTS 1:50K maps. In the upper right corner it says "t2 MyTopo". "My Topo" is the name of the tile server. Click the drop down, and quickly look at some of the different maps. The most important choices are "t2", "t5", "t4" and "t8". Those codes are just what Google and GMap call them. They correspond to tile servers. A tile server can vary which maps to serve depending on your location. So what you see for each choice of server depends on your province. For example, choice "t4" is labelled "CalTopo High Res USA", but in BC it serves up the 20 meter TRIM data.

  Here's something people get mixed up on. On a smart phone, I often browse to the Bivouac site to look at mountain pages, road pages or trip pages. This is often my first step to downloading the .gpx file. However, I never use Bivouac Gmap itself when on the phone. The phone doesn't have enough power. Some people naturally think that GMap must be where you get background maps for your GPS. But it isn't. To get the background map onto your GPS you need to download it from within the GPS app itself. Once you've done that, THEN you can download the gpx OVERLAY by browsing to Bivouac on your phone browser. It's really simple because the browser dumps the .gpx file into your "downloads" folder, and that's where the App expects to find it.

Another source of confusion is what to call the various data sets. For example, the NTS 1:50,000 maps are called "CanMatrix" in BC Navigator, and on the Garmin the TopoCanada contours are from that same data. One really confusing thing is that in Bivouac GMap, choice "t4" is labelled "Caltopo Hi Res USA", but in BC this is the TRIM data. In the USA it is the 1:24,000 maps. Caltopo is the name of the server, but what data you get depends on your location. The table below shows how the same map data has different names in different devices:


 Government Gmap Garmin BCNavigator Gaia ---------------------------------------------------------------------
  NTS 1:50 t2-MyTopo TopoCanada Canmatrix CanadaTopoWest
  NTS Topo Can t5-topo Can TopoCanada CanadaTopo
  BC TRIM t4-Caltopo n/a Caltopo n/a

Note that there are many free phone apps that have contour lines that appear to have contours that are different from the old NTS contours. Some might even appear to have more accurate data. But don't be fooled. These are either interpolated from the real 100 foot contours, or they are created from various Space shuttle Digital Elevation Models. Neither are as good as the real NTS and TRIM contour lines.

Note that in addition to actual maps, there are also various servers with satellite data, and some phone Apps can cache this as well.


Comments

#6055 - 2017.05.12 Robin Tivy - Direct Browse on phone versus he Email of .gpx files
Ryan says he goes to Bivouac (on his computer?) and emails himself the .gpx file to get it on your phone. What I do is directly browse Bivouac on my PHONE when I've got wi-fi, and then click on whatever .gpx links I want. That puts the .gpx file in the downloads folder on the phone, and then when I go into Backcountry navigator to "import" the file, it knows exactly where it is. This is for android phones, not sure about "downloads" folder concept on iPhone.

#6054 - 2017.05.12 Ryan Allderman - Open Street Map
Yes, I agree. Before a trip I go to Bivouac or other sources and down load the gpx files I need. I then e-mail them to my phone, go to my phone and click on the files in the e-mails and open them in the OSMAnd app. The tracks will then be on the map to assist with navigation.

Where the embedded trails are a big help is when I haven't planned a trip and find myself lost. Often a nearby trail will be on Open St Map and I'll find my way home.

Another trip planning thing I do is create a Map on Google My Maps https://www.google.com/maps/d/u/0/ these maps can easily be shared with other contributors in order to collaboratively plan a route. The maps are also available offline if Cached (just view the map at all zoom levels before going offline) first.

#6053 - 2017.05.12 Robin Tivy - OSM: Embedded trails versus Overlay
The OSM (Open Street Map) layer is worth special discussion. You can see what I'm talking about by going to any Bivouac GMap and choosing "t8 Topo World OSM Cycle" in the upper right corner. The basic idea of OSM is to "embed" the trails right into the image of the base map. This is a different approach than the "overlay" approach used by Bivouac. In Bivouac, the roads and trails become an "overlay" for any base map you want. So you can see the latest trails against a 1:50,000 contour map, or against a satellite image. The idea of "overlays" is a standard GIS concept.

Another issue is audit trail. With OSM, you don't know where they come from. Are they based on a track log? Or just copied from an old 1:50,000 map? How accurate are they? Some areas are very good, but others are not so good. I've come across numerous cases where the trails don't fit together as a coherent network.

Both approaches have advantages. The "embedded" approach is simple, and you don't have to learn how to download .gpx files. But ultimately, the overlay approach is far more powerful. You have more control over what layers and objects you display on your map. And because each trail becomes a "track log object" on the GPS, you effectively have a little database in your pocket. Having that database is very powerful. For example, already on the Gaia app, you can click on a Bivouac trails and read a trail description. Ultimately, your smart phone could become a complete pocket guidebook. I'm still trying to educate several smart phone developers to understand that concept, so we'll see.

#6050 - 2017.05.11 Steve Grant - Gmap offline
You can sort of store Gmaps on your phone by taking a screen shot of whatever you want to have with you from Gmap. It might take several to capture what you want in sufficient detail. Of course this is not interactive but you can compare it with your live offline map to figure things out.

#6048 - 2017.05.09 Ryan Allderman - Smart Phone Apps
I use Google Maps, Google Earth and Google My Maps (Create custom maps with tracks), I cache the satellite and terrain views before a trip. The satellite view is particularly helpful when navigating micro terrain.

Another app which is very helpful is OSMAnd, it has downloadable vector versions of the Open Street Map data, contours and hillshades are available but not very high resolution. The great thing about Open st maps is that it is continuously updated by everyone so very many of the BC hiking trails are on there. If a trail is not there you go to the Open St Map site and add it and it will then be in the next months download for BC or where ever. This app has got me unlost many times in a few countries thanks to the inclusion of often obscure trails.