LATEST: New in version 2.15 is an on-line Help Page that requires users to register for automatic logon.
TerraIncognita  (about $30) does not require Global Mapper (about $300) to convert Google Earth .jpg files into a single Custom Maps .kmz file.  This version allows one to select the size and number of tiles (100 Max as required by Garmin) to produce a single .kmz Custom Map file directly.

GENERAL:  Garmin claims you can create Custom Maps in five easy steps (HERE).  'Your mileage may differ,' but using Google Earth to create Custom Maps was a time-consuming pain for this reviewer.  For those interested in the highest-possible resolution aerial photo maps for Garmin's Custom Maps, the tool of choice is TerraIncognita.  This program will automatically download Google Earth, Bing, OpenStreet, and other maps.  These maps can be GIS-registered for Ozi Explorer,  ArcView, TrekBuddy, or SmartComGPS maps.  TerraIncognita is an updated version of GoogleOzi.

SELECTING A MAP FOR CUSTOM MAPS:

SETTINGS:

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Set General, "Overlay saved" to 0 to prevent overlap. °  Set "Opengis kmz map (save)" as shown for Custom Map limits

NOTE: Garmin suggests Max Tile size of 1 MPx, but 4 MPx can be used without noticeable reduction in resolution.
(This allows a photo of 2,048x2,048x100 (419,430,400 pixels) to be processed.)

CREATING MAPS:

"Selection" refers to the type of map boundaries you can draw with the mouse.
('Select all' is used when importing OziExplorer .map files which allows one to select the whole map)

Use the mouse to draw an area of interest.

NOTE:  The zoom level here is "250m" which corresponds to 4m/pixel (bottom of screen).
"Zoom level": 100m = 1 pixel/meter, 50 = 2 pixels/m,  20 = 4 pixels/m,  10 = 8 pixels/m (the highest available on Google Earth).

Next select Zoom level "10m"  0.125m/px (8px/meter).  If no map is displayed, one must use a higher zoom until a map is shown.
The Zoom levels dropdown menu (and tray) will show the zoom level.

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WORKING WITH "Opengis kmz map":

WORKING WITH "ArcView map":
The advantage of creating an ArcView map is that it results in only ONE .jpg file which can be enhanced (see Improving Screen Display) and converted to a .kmz file by the $5 program, G-Raster.   The disadvantage of G-Raster is that it can't handle a file greater than 100 Mpx.

Improving GPS Screen Display:
Before loading the .jpg file into G-Raster, it's best to run them through Photoshop Elements for Color Correction, Brightness (increase it by about 35% to make them more visible in the units and Google Earth).  It's also helpful to use Filter, Sharpen, Unsharp Mask (Amount 30%, Radius 10, Threshold 0).  Save the jpg image with the original filename.

In G-Raster, select "ESPG File".  Select "Load ESPG Raster With Worldfile."  Insert "ESPG Code" of 3395.  Process Raster Graphic. Create KMZ file.

WORKING WITH "OziExplorer map":
Here the size of the area selected isn't restricted.  TerraIncognita will create several .map files depending on the size of the areas.  Once the .map files have been created, they can be accessed by OziExplorer where waypoints, tracks and routes can be displayed and created.  (Also see Global Mapper, below.)

USING Global Mapper ($300, but has no limitations):
Load all the Ozi maps into Global Mapper at once which Global Mapper can then convert into a single .kmz file.  This is done by selecting the "GPS" dropdown menu, "Send Raster Maps to Connected Garmin Devices", and check "Display on top of Roads and Trails" box, OK.  Global Mapper can then convert the OziExplorer .map and .jpg files into a single .kmz file with no more than 100 tiles for Custom Maps.    Save the files to a PC folder for later uploading to a GPS unit that supports Custom Maps.

LOADING WAYPOINTS, TRACKS AND ROUTES:
Implemented file formats are: OziExplorer *.plt, *.wpt, GPS eXchcange Format *.gpx, Nmea0183 log *.nmea.
NOTE: You don't have to buy OziExplorer in order to save your Garmin waypoints as .plt files.  G7ToWin (shareware) can convert the Garmin .gdb track files into .plt files and waypoints into .gpx files.  (TI will not accept .plt or .gpx files that are 'mixed' tracks and waypoints.)

After waypoints or tracks are loaded by: File, 'Load waypoints, tracks, routes', the Waypoints, Tracks menu items are enabled.
All can be hidden in menu Waypoints,Tracks by unchecking Visible. Or individually each waypoint or track can be hidden in waypoints or tracks dialogs. Waypoints table menu will show a list of loaded waypoints. This window can always be visible during browsing the map.
Tracks table contains all tracks loaded from files. Both windows can be visible all time and can be closed by [x] on window or unchecking in menu.

The first two icons in both dialogs are to show or hide selected items in list.
Compass button (3rd) is to locate selected waypoint or track, it is the same as double clicking on item in list.
Waypoints can be sorted by name (4th button) or by distance (5th button) from current center of map in main window.
In the Tracks menu, colors can be changed by the (4th) button.
Default colors of waypoints or tracks can be set in settings dialog.

All waypoints and tracks are deleted on closing the application.

CONCERNING IMAGE QUALITY:
Global Mapper will complain that some combinations of  .jpg files are too large to conform to Garmin's Custom Map hard limit of 100 tiles and suggestion they be no larger than 1024x1024 pixels each.  However I've been able to create a .kmz file from 400Mpx of Google Earth high-resolution images without significant loss of resolution in a GPSmap 78sc.  But this may be the limit.    The test is to look at the number of pixels in each of the created .jpg files with Windows Explorer (Select Dimensions under Choose Details).  The sum should be no larger than about 419 Mpx -or 100 2,048x2,048 pixel squares.  This will create a file about 115MB.

Now don't get lost out there -youall!
jack yeazel