Garmin eTrek Vista vs. Dakota 20 vs. Oregon 450

[Boyd]

Yes, you can enable the 100k topo along with a third party map, and the shaded terrain will be applied to the third party map. I had an Oregon 400t (earlier version of the 450t) and did this often myself. Downside is that it slows down GPS performance because it is drawing the hidden Garmin map along with the other map.

It should also be noted that the exact way this behaves is dependent on the third party map. Maps have a draw priority assigned by the author. Maps with a higher priority will cover up lower priority maps. So if the third party map has a lower priority, the Garmin map would cover it up. My experience has been that most third party maps will cover the Garmin map however.

All things being equal, if you want the Garmin 100k map then $35 is a good deal. Even better, the 450t has 4GB internal memory (the 100k map is almost 3GB) while the 450 only has about 1GB. So even if you don't use the Garmin map, you would get more storage space. I would only suggest that you shop around at places like Amazon and GPSCity, because I have no idea how competitive WalMart's price is on the 450 and that could tip the balance.

[Boyd]

However, zoomed out past 800 ft the gpsfiledepot maps look confusing with squiggly lines and the shaded relief from Garmin U.S. Topo starts to be quite helpful (I'm in the Rocky Mountains area).

You really can't generalize about "the gpsfiledepot maps". They are created by many different people using different technicques. Garmin's format allows for something called "custom types" whereby an author can have a lot of control over the appearance of each object on the map.

Of course, many authors don't bother and just use the default Garmin style. And the 100k Garmin topo  just uses the default styles too (this means the map will look different on different model GPS'es, whereas custom types give a consistent look). One thing I dislike about the default style is that small roads are a grey color that tends to disappear into shaded terrain.

The behavior of shaded terrain on the basemap is different from the high(er) resolution data on the 100k topo. The basemap shading will only be applied when you zoom farther out. This is done because the shading is low resolution and would look bad when zoomed way in. The 100k map shading should appear at all zoom levels. If you get one of Garmin's 24k maps, the DEM data (shading) is even higher resolution and looks much better at closer zoom levels than the 100k.

[Seldom]

Screen clutter can also be caused by the detail level setting on the GPSr, and by the "EndLevel" that the map author sets for various data types.  If everything is drawn at the widest zoom level then the map could be unreadable.  Both of these apply with or without the DEM Basemap being enabled.