Multiple maps enabled on the eTrex 30x

[Tony_s]

New GPS user here and this may be a silly question but is one of the enabled maps the default if I have all three enabled? I have TOPO US 100, Worldwide DEM and an AZ TOPO (which I believe is higher quality than the US TOPO version).

[Boyd]

Maps have something called "draw order" which is specified by the author as a number between 0 and 31. These behave like layers in Photoshop where higher draw order maps cover up lower numbers when they are enabled at the same time.

The basemap will always be drawn behind all other maps. Not sure about newer versions, but my old copy of the 100k topo has a priority of 20. Not familiar with the AZ topo, but if it has a priority of 21 or greater, it will cover up the 100k map. If it has a priority less than 20, you will not see the AZ topo if the 100k map is enabled.

As a generalization, you should only enable one map at a time unless you have a specific reason to do otherwise. The GPS will respond more slowly with multiple maps enabled since it must also draw the hidden ones.

One reason you might want to enable the 100k topo in addition to a GPSFileDepot map is shaded terrain however. Garmin's 100k and 24k topo maps include special data that creates shaded terrain on most GPS units and full 3d views on certain models. The method for creating 3d terrain has never been "cracked" by third party authors, so none of the GPSFileDepot maps will have that feature.'

But if you enable the 100k topo map at the same time as a GPSFileDepot map, the 3d terrain will be added. For this to work, the GPSFileDepot map must have a higher draw priority than the 100k map however.

Another reason to enable two maps at the same time would be the special case of a transparent overlay, such as the MyTrails map here. That map only includes the trails and POIs, so it doesn't have much value unless you also enable a topo map at the same time. When you do, the trails are added to the other map.

[Tony_s]

Thanks! Good info.

So is the draw information easily found in most maps?

[Boyd]

This is normally something that only a mapmaker would deal with. You could use Popej's gmaptool program to view and change the draworder of a map, but this is not an especially user-friendly program that is intended for advanced users, so I would not advise messing with it.

For the average user, it pretty much "is what it is", and it's obvious which maps have higher priorities by observing what happens when you enable more than one on the GPS.

Note that Garmin's City Navigator map has a draw priority of 30. The 31 priority is used for transparent overlay maps like MyTrails. This enables them to work as overlays with City Navigator.