Does anyone have the "DEM" option turned on?

I have it, or at least had it, on my Garmin Zumo XT. I may have either deleted it or put it in another folder so that it doesn't pop up when I change maps.

This is a map that contains elevation data for whatever region is on your GPS. This will vary by device, but pretty much all Garmin units can display elevation using either that map or data from the satellites. There will be an option somewhere in the menu for that. Now, the resolution of the DEM map is unknown and may be different on different devices. But my own experience (from the Montana and Oregon series) is that it's probably medium-resolution 1/3 arc-second data which has a resolution of about 10 meters (33 feet). That means (in theory) there is an elevation reading to correspond with each 10-meter x 10-meter area on the map.

But 1-meter high-resolution data is now available for much of the US. This is an example (which has nothing to do with Garmin) from my own site showing terrain modelled at 4-foot resolution. You can see the elevation displayed at the top left as you drag the map around. You can zoom in and see quite a lot of terrain detail

https://boydsmaps.com/#12.00/43.773331/-71.257164/midatlidar...

For even more fun, I have the option to view it in true 3d, which really shows what can be done with high-res DEM data

https://boydsmaps.com/#13.00/43.765097/-71.257203/mbx3dmidat...

I used the highest resolution data available for each location - here's an example where only low resolution data was available. I believe is is comparable to Garmin's DEM maps, the resolution here is about 32 feet. Notice how there is much less detail.

https://boydsmaps.com/#13.00/43.985509/-73.683436/midatlidar...

I remember the Nuvi started including a 3d DEM basemap at some point. IIRC, that was very low resolution, like 1 arc-second (about 30 meters / 100 feet or maybe even less). That would have little real use IMO, but it was able to create shaded terrain that looked cool when you zoomed way out.

The other way to get elevation data is from the satellites themselves. This is notoriously inaccurate and can easily be off by over 100 feet. That might not matter a lot on top of a 5,000 foot mountain but in the low coastal area where I live, GPS elevation often shows me as much as 100 feet below sea level. IMO, that is all but useless but others might disagree.

Now, there is one more way that Garmin handheld GPS units can determine elevation. Some of the better models also include a barometric altimeter for taking actual pressure readings. This was a sought-after feature for many years, but that was before we had high-res digital data. Maybe I just never learned how to use it, but you need to calibrate these altimeters pretty often. I did an informal test some time ago, walking up and back down a mountain. I calibrated the GPS when I started and by the time I returned to my car, it showed a completely different reading.

So, personally I'd trust the DEM a lot more than these other methods. But do you really care about elevation? In the car, it might be of some interest driving up and down hills, and probably doesn't need to be terribly accurate for that. On foot, the elevation profile of trail or track can be something interesting to have and might help choose the easiest trail to follow.

Probably much more than you wanted to know, but I have worked extensively with elevation data.

That’s some great info. I remember when the DEM map made its appearance on the nuvi. Made for some great visuals but other than that, it was kinda pointless.

I remember being very excited about the Nuvi DEM basemap when it came out. IIRC, my first device that had it was a Nuvi 5000 - with big 5 inch screen! I started a thread about the basemap over at gpsPassion, I think it was called "Around the world with the new 3d basemap", or something like that and there were a bunch of screenshots. Here are a couple:

https://stephencreek.com/gps/basemap/screenshot52447.jpg

https://stephencreek.com/gps/basemap/screenshot53846.jpg

Now, I also have a low resolution 3d map at boydsmaps that covers most of North America which is based on something called ASTER GDEM. That's and acronym for Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model - quite a mouthful! It was created by a satellite that scans terrain. I made a low-resolution US topo map from this data here. This is the same location as the Garmin screenshot above, for comparison. Even though it's low resollution, you can zoom in farther than the Garmin basemap

https://boydsmaps.com/#9.00/43.700650/-73.203804/lctopo/0.00...

https://boydsmaps.com/#8.00/44.483776/-110.566933/lctopo/0.0...

But basemaps are supposed to be low resolution, and they are different from the DEM datasets that Garmin has on their "serious" topo maps. Here's some more information about the two datasets that I am using at boydsmaps

https://boydsmaps.com/mapinfo/elevinfo.html

I wrote my own app for exploring 3d terrain that has lots of realtime controls to play with. Here's an example of the Lake George area

https://boydsmaps.com/terra/#43.700650/-73.203804/0/124999/0...

Same location in 3d

https://boydsmaps.com/terra/#43.700650/-73.203804/1917/1258/...

You can zoom way in on these - click the "1.5" button under "Map Size" to load the highest resolution map data. Try just playing around with the sliders to see how lighting affects what you see. The vertical exaggeration slider is also fun.

I should also mention, in case it isn't obvious, that on all my 3d maps you use the right mouse button to tilt and rotate the map. Hold the button down and drag left-right to rotate or drag forward/backward to tilt the view.

(Caution - this has crashed on all the phones I've tested, but mine are old. You need a computer because of the processing demands. It crashed on my 2018 iPad but works on my m4 iPad Pro, FWIW)

WOW Boyd. That's some real in depth info. Thank you for the explanation.

I didn't know that it was an option. I will check it out. Is it on the settings page?

The OP has not said what kind of device he is using. As I've mentioned, I no longer use Garmin devices but have a big box of old ones. Anyway, some devices may have a map called gmapdem.img if you look inside the Garmin folder while connected to your computer. With newer devices, that file may be in the invisible .System folder and you will need to show hidden files to see it.

But I think those devices will also have a menu option to enable/disable the DEM map. And yet, I don't see this on any of my own units, I looked at my DriveSmart 61, DriveTrack 71, Nuvi 205 and Montana 600.

I used to have Garmin's 24k topo installed on the Montana and the DriveTrack has the US 100k topo pre-installed. But I removed those maps myself to make room for others. I *think* these devices had the gmapdem.img file on them originally but I deleted it.

I'm fairly sure that the DEM data is part of the basemap on current automotive units (gmapbmap.img) and is very low resolution data that only appears when you zoom way out, as discussed earlier.

A quick Google search suggests that current cycling and outdoor Garmin devices with pre-installed topo maps may include the gmapdem.img file, but I have no experience with these. Look in the map settings and there is (probably?) and option to enable/disable it.

I should add that Garmin uses a proprietary format for their DEM data which baffled people for years. More recently, someone at openstreetmap (?) finally reverse-engineered the file format and some people are now making 3rd party maps with DEM data. But all the examples I've seen are using very low resolution DEM and the process for creating it is complicated.

...through my crate of old Garmin devices and found a Nuvi 5000, Dezl 760 and Nuvi 3550. The Nuvi 5000 did not have the gmapdem.img file. I couldn't get the Dezl to go into USB disk mode at all for some reason. But - bingo! - the Nuvi 3550 does have the gmapdem.img file which is 624 MB. It also has a gmap3d.img file. IIRC, that file contains 3d buildings and other 3d features.

I think the difference here is that the Nuvi 3550 featured 3d terrain in normal driving view. That was only available on some select models (IIRC, the Nuvi 3790 was the first model with this feature). Anyway, on the Nuvi 3550 if I go to the Map & Vehicle Menu > Map Layers, there's a checkbox for 3d Terrain which turns the DEM map on and off. But just to make it more confusing, if you go to Map & Vehicle > myMaps You can also enable/disable the DEM map by checking the box that says North America DEM, which has the same effect.

So, that will enable/disable the 3d terrain view on this device. But AFAIK, there are no settings to use the DEM map instead of GPS satellite data for elevation. It is only used to provide a 3d view.

Found these, from an old post I made at GPSReview. This is an example of the 3d map view on my Nuvi 3790

https://stephencreek.com/gpsreview/3790/3d02.jpg

Now - just for fun - compare that to my high resolution 3d view of the same location (Mount Desert Island) and you'll get some idea of how little detail the Nuvi terrain had

https://boydsmaps.com/#14.00/44.333832/-68.249884/mbx3dmidat...

Here's another example

https://stephencreek.com/gpsreview/3790/3d07.jpg

FWIW, this is my own low resolution 3d view of the same place.

https://boydsmaps.com/#12.00/41.001617/-123.892036/mbx3dnalc...

But Garmin does have cool 3d buildings!

https://stephencreek.com/gpsreview/3790/3d03.jpg

Under my maps, I have North America DEM selected. Haven't the foggiest of what it does or doesn't do. It came like that when I got this unit, and it gets me where I need to go. Just afraid to mess with something that works!

According to the specs, the DS 86 has 3d buildings and terrain.

https://www.garmin.com/en-US/p/720310/#specs

I think the menus will be like the ones on my Nuvi,

Settings > Map & Vehicle > Map Layers

As mentioned above, you could also un-check the DEM map under myMaps and it will have the exact same effect as the Map Layer setting.

If you enable the 3d terrain in the menu, you should see hills and valleys in 3d view on the map. I think it will also show shaded terrain in regular North Up or Track Up view. If you are in a relatively flat area, then you won't see anything however.

Either way, it will certainly do no harm to turn that map layer off. Doesn't do any harm to leave it on either. If you're curious, try it both ways.

updating my own knowledge, from google AI:

In a Garmin navigator, "North America DEM" stands for Digital Elevation Model, and its primary job is to provide 3D terrain shading and elevation data across the North American continent.

Instead of showing roads, it maps out the physical curves and shapes of the Earth's surface.

Core Functions of the DEM Map3D Shaded Relief:

It adds visual depth to your navigator by rendering shadows and contours over hills, valleys, and mountains.
This helps you see the actual topography of the surrounding landscape while driving.

Elevation Tracking:

It tells your GPS exactly how high above sea level you are at any given point. It is also used to help calibrate the built-in altimeter on certain outdoor models for more accurate height readings.

Low-Zoom Basemap:

When you zoom far out on your map (typically to 5 miles or higher), the Garmin hides complex street data to prevent clutter and switches to this elevation data to keep screen updates smooth and readable.

Should You Keep It Enabled?

Yes, you should keep it checked. It works in the background alongside your standard road maps (like CN North America NT).

Turning it off won't break your standard turn-by-turn navigation, but your map background will look flat and featureless instead of 3D.

For more details on how your specific automotive model handles background layers, you can check the official Garmin Support Page.

Nice to see that Google AI supports and confirms all that you have been telling us!

Google AI most probably "learned" all of this from Boyd and others here and elsewhere (when everyone else figured it out years ago). I also know that Boyd wouldn't knowingly provide false info.

Humans will always be the best source.

...in their day, for this kind of info. I was thinking the same, that Google AI (aka Gemini?) might have been trained on archived copies of those old sites.

But that knowledge only goes so far and it's arguably a whole new ballgame with Garmin (apparently) embracing a custom version of Android for new devices like the DriveSmart 86.

But this is what I find very interesting. Garmin's automotive/recreational units are now nothing more than Android apps. But, of course, they jealously guard the software instead of selling it for us to install on our own devices. That seems short-sighted to me, but I guess they make a lot of money on the hardware.

I display the elevation in the bottom right corner, but I don't know if that's what you're calling the elevation map.

I find it interesting, to see the changes.

..on what your GPS is. If it's an automotive device like a Nuvi or DriveSmart, I'm pretty sure that the elevation you see is always calculated from the GPS satellite data. As I mentioned earlier, that is very inaccurate and it's common to see errors of 100 feet or more. GPS is good at finding horizontal position, lousy at finding vertical.

On a handheld or (maybe) a device like the Tread, there may be an option to use the DEM map as the source for elevation. It would then depend on how accurate the DEM data is in Garmin's map. As we've seen above, their data is pretty low resolution, but in some cases it may still be more accurate than satellite-derived elevation.

[edit]See this Garmin FAQ. Regarding GPS elevation, they say "Elevation calibrated by GPS is accurate to +/-400 feet at any given point with a strong GPS signal. "

https://support.garmin.com/en-US/?faq=WlvNrOungC28xGtwB7hLY5

It's very flat where I live in southern NJ, in fact the highest point in the region is only about 250 feet. So, I could be on top of that and might get a gps reading that is 150 feet below sea level and the GPS would be performing as expected, LOL