Garmin DEM (Digital Elevation) Maps
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      16 years
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I was doing some searching through Garmin's faqs and came across this one:
https://support.garmin.com/support/searchSupport/case.faces?...
As I thought about this, I was shocked to see "DEM basemap" offered on some pretty ancient Garmin GPS devices like the old nuvi 8x5 series.
The more I looked into this, I've decided that Garmin has complicated things for us by calling two different features DEM.
What we currently mean when referring to DEM maps is possibly what Garmin calls in this faq "includes 3D terrain" and its data is stored in a separate file in the nuvi with the filename gmapdem.img. This form of DEM map appears live on the navigation screen at all zoom levels on the more recent more advanced devices Garmin offers:
https://support.garmin.com/support/searchSupport/case.faces?...
Note however, that Garmin also offers a "plain" DEM on many older units including on several very old GPS series. This DEM map does not display live while navigating but requires a tap on the map to display a static map, then zoom out to 5 miles or more to see the DEM displayed.
In looking at my old nuvi 855 and 2460, I don't see a separate file for this "plain" DEM map so the DEM data must be embedded in either the basemap or the City Navigator map. I unchecked my City Navigator in these two nuvis and found that this DEM map is retained so my guess is that the DEM data is built into the device's basemap along with major roadways and such.
I mention this here because I don't remember any past discussion of the two types of DEM maps so I thought I'd share my observations to possibly prevent future confusion.
Does this seem correct?
Note: I realize that by writing "DEM maps" I'm actually writing Digital Elevation Maps maps, but it just didn't seem right to write DEM without adding a "maps" after the DEM. 
World basemap
CraigW,
The DEM (elevation display) on these older models is part of the world base map (gmapbmap.img). It only shows when you zoom way out on the 2D map. At some zoom level, the display switches from using the City Navigator map to the World Basemap, and this map shows the DEM shadings for mountains, etc.
The basemap has very little detail, showing only major roads and cities, but it does have the DEM shading.
Alan - Android Auto, DriveLuxe 51LMT-S, DriveLuxe 50LMTHD, Nuvi 3597LMTHD, Oregon 550T, Nuvi 855, Nuvi 755T, Lowrance Endura Sierra, Bosch Nyon
Yup
CraigW,
The DEM (elevation display) on these older models is part of the world base map (gmapbmap.img). It only shows when you zoom way out on the 2D map. At some zoom level, the display switches from using the City Navigator map to the World Basemap, and this map shows the DEM shadings for mountains, etc.
The basemap has very little detail, showing only major roads and cities, but it does have the DEM shading.
Yes indeed. I guess the confusing part for me was that the new "DEM," which Garmin calls "3D terrain" has a filename of gmapdem.img and at least here, we're calling it the DEM map based on the filename.
We wouldn't even be discussing this if GarminMapUpdater didn't go and delete or disable the new 3D terrain map each time its used to do a map update.
At least now Garmin Express is an acceptable option allowing most or all of us to no longer need GarminMapUpdater.
855 DEM
On my 855, it seems to switch to the elevation view at the 5 mile zoom level.
Alan - Android Auto, DriveLuxe 51LMT-S, DriveLuxe 50LMTHD, Nuvi 3597LMTHD, Oregon 550T, Nuvi 855, Nuvi 755T, Lowrance Endura Sierra, Bosch Nyon