About digital maps and Garmin
The digital mapping files on Garmin devices contain two very different kinds of data that serve quite distinct purposes:
- Map image tiles
Digital images that are used to present a view of the map around your current location. Since the maps are zoomable, the map data must include images for each available zoom level. (The images are stored in the form of a lot of 'tiles' - square .jpg images, each covering a small area. I only mention this for interest, you shouldn''t need to know about the tiles).
A description of the road (and track) network in the form of a linked network of geographic points, together with details of the type of each road and even their names. This data is used both to generate new routes, when needed, on the device itself and to give instructions for turns at junctions, etc.
Most of the types of digital map that we shall be discussing provide both kinds of data, but there is one type, called 'Topographic' or 'Topo' that do not include any road network data. Topo maps are intended for cross-country walking where roads are unimportant. They can be used for cycling navigation together with a pre-loaded route derived from a web mapping system, but the navigation instructions will be quite primitive (such as 'Go Southwest', etc. at every turn in the road, whether at a junction or not). Useful nevertheless if nothing better is available.
Sources for maps
Maps available from Garmin
Garmin offer several types of digital maps for use with their devices. We'll discuss the various types of Garmin-supplied maps here only briefly because my preference and the focus of this course is on the use of OpenStreetMap/OpenCycleMap as an alternative that offers some advantages, which in my opinion go well beyond the obvious cost savings.
Base map: The device itself includes a 'base map' that is built-in. The base map includes only the network of major roads throughout Europe and a few large geographic features. It is very unsuitable for cycling use since hardly any of those roads are suitable for cycling and many prohibit cycling.
Topo maps: see above. The visual rendering isn't attractive, but the amount of detail is high. They're probably derived from Ordnance Survey in the UK, IGN in France, etc. No ge0data is included, as discussed above.
City Navigator maps: These are the same maps used in Garmin's car SatNav devices. They do include a lot of geodata as well as map tiles, but the geodata often leaves out key information useful for making good cycle routes, e.g. roads with cycle lanes, gaps in road barriers, off-road cycle trancs and the Sustrans routes in the UK.
Ordnance Survey maps: These have recently become available for use with Garmin devices, but amongst the cycle-specific devices only the Edge 800 is compatible with them. The map images are of the same very high quality as OS paper maps and they should include a quite a lot of the Sustrans National Cycle Network (as shown with green dots on OS maps).
I've no direct experience of using them. A friend who has been using an Edge 800 for a while tells me that the routes it generates (i.e. when making routes on the device itself are not good for cycling. That doesn't surprise me, because good cycle route generation requires a lot more information than just the well-known cycle routes.
OpenStreetMap is actually a very large geographic database generated and maintained by a huge number number of voluntary mappers. The database is stored on a set of internet servers and is updated continually by volunteers. (We'll say a bit more later about becoming an OSM mapper. It's much easier than you might imagine and you can start by just adding a couple of features). The use of the OSM database and maps derived from it is entirely open and free (http://www.openstreetmap.org/copyright/. If you follow the link you will see that some data has also been contributed by national mapping agencies, including Ordnance Survey. Their contributions are under the same terms).
The OpenStreetMap database is used for many purposes. The most obvious one being the generation of maps for display on screens or for printing. The map that appears at http://www.openstreetmap.org/ site is just one of many different renderings. You can see some others by pulling down the menu at the top right under 'Standard'. One of those is 'Cycle Map' which is the result of an initiative to make sure that all the signed cycle routes (Sustrans, local authorities, etc.) are included and tagged as such in the OpenStreetMap database. You can access the same OpenCycleMap at http://www.opencyclemap.org/.
Another use for the OpenStreetMap database is to produce sets of map tiles and geodata for 'routing engines' and GPS devices (Garmins, phones, etc.) that are capable of calculating routes. There are quite a few sources for such datasets each with slightly different characteristics, but the most useful one (in my opinion) for cyclists was produced by same person who initiated the OpenCycleMap extensions to the OpenStreetMap database. His name is Andy Allan and he maintains an online shop where you can buy SD memory cards containing OpenCycleMap datasets for a range of European countries, specifically designed for use in Garmin devices. He also offers a wider range of datasets for download and copying onto your own SD card. At the time of writing there were SD cards available at £15.99 for:
- UK + Ireland
- Austria + Switzerland
- Benelux (Belgium, Netherlands, Luxembourg)
- North Germany
- South Germany
and downloads available at £9.99 for:
Possible issues with the use of OpenStreetMap/OpenCycleMap
- Completeness. The most obvious question is 'how complete and accurate can a map made by a load of volunteers be?' The answer, in my experience is extremely so for the UK and most of the parts of Europe I have cycled it, although there can be occasional glitches and missing features - even missing roads. Obviously I haven't done a comprehensive check and in any case features are being added and corrected all the time. In the UK the coverage seems better than 99% for roads and cycle tracks. The Netherlands is even better, thanks to a donation of data from the Dutch national mapping agency. I wouldn't expect the coverage in a remote part of Spain to be very complete (perhaps only 50% of rural roads were there the last time I was in Andalucia 3 years ago, on a quick check there seem to be >70% now). Surprisingly, when you're following a pre-planned route that you have download from a web mapping service, the absence of a small feature or a road from the map isn't a very major deal. You still see the route and your position on it against a background that includes most roads and other features, so decisions at intersections are still usually straghtforward.
- Glitches in the display and use of OSM/OCM data on Garmins. When navigating a route, the mauve line representing the route is sometimes temporarily obscured by a thick black line representing a road. The work-around is to zoom out until the mauve line reappears. These black lines shouldn't be there. They seem to be a consequence of the combination of OCM mapping and Garmin hardware.
- Issues when using routes provide by some routing engines. These may include false instructions to turn off onto a nearby parallel road and even false instructions to turn around and go back. This happens only very infrequently. It seems to be due to the way in which the Garmin tries to interpret the route and issue instructions. If it becomes a problem, you could switch off the turn instructions and just follow the route as it is shown on the map:
Settings > Routing > Guidance method > Off Road
Acquire an OpenCycleMap SD card or a downloaded dataset and load it into your Garmin device.
To make the new map appear on your device, you may need to choose it:
Menu button > Settings > Map > Map Name > OpenCycleMap (select)
Note that the map doesn't look the same as the one at http://www.opencyclemap.org/. But it contains the same information, with a colour scheme and feature renderings determined by the Garmin.
Downloaded UK maps from OpenCycleMap shop (SD cards out of stock) to Mac and unzipped ukireland.zip to yield 705Mb gmapsupp.img file.
Bought 2Gb microSD card from Maplins, inserted into Edge 800, connected to Mac USB port. Garmin and SD card appear as 2 volumes, 80Mb and 1.99Gb respectively. Copied gmapsupp.img to SD card and ejected both volumes.
Booted Edge 800, navigated Menu/Settings/System/Map/Select Map. Display shows INTNL Standard Basemap as enabled; no other option visible.
Downloaded the Benelux, North and South German maps to my Mac. The ZIPs have different names but their contents are all gmapsupp.img files. Copied the 4 IMG files to separate folders within /Garmin on a 4Gb SD card, but the Edge ignores them after boot.
Moved the British Isles IMG file into /Garmin and rebooted: the map gets used.
Inference: to cross from one map to another I need to move/rename IMG files; ie use a computer.
I'm using a separate SD card for each country gmapsupp.img file. I have tried loading multiple maps with different names but that didn't work on my Edge 605 - only a map named gmapsupp.img is visible.
However Shaun, who has an Edge 800 says:
'Even better I have 3 images (UK, Benelux, and South Germany) on the same SD card. The format of the file name should be 8.3, i.e. up to 8 ascii characters and then ".img" for the Garmin to read it. '
I infer that on the Edge 800 you should be able to rename the files e.g Benelux.img, etc. and put them all in the Garmin folder.
This post has 1 feedback awaiting moderation...