First off, I apologize for fixing the screen width so wide.  As I was playing with the page layout, I decided that I preferred a fixed layout for the screen dumps over more readable text.  This page is graphically intensive and will take about five minutes to download with a 28.8kbps connection. 

MapSource Data & Resolution Comparison

Here is a comparison of the screen displays on the Garmin GPS III Plus (software revision 2.01 (except for the Topo CD, which uses revision 2.02)) centering on 1600 Pennsylvania Ave. in Washington, DC -- an address that may be familiar to you.  All data elements were set to "Auto", with the exception of waypoints, which were turned off and street labels which were set to 500 feet.  The device was set to simulate mode to remove Selective Availability drift and to make the EPE circles comparable.

• Examples using the U.S. Roads & Recreation CD use the MapSource maps for District of Columbia, Arlington County, Fairfax County, Prince George's County, & Montgomery County.  These maps took 1440K, which is the exact amount that the GPS III Plus can hold.  I had to exclude Alexandria Township, which was a small file that wouldn't fit, and you'll see the impact of that decision below.  I created examples using all five preset resolution modes:  ("Most" mode followed by "More", "Normal", "Less", "Least").
• Examples using the Topo CD use various MapSource maps surrounding Washington.  The memory could only fit five selections, which you can see below.  Revision 2.02 of the MapSource software uses large icons for points which were dots in 2.01, so I selected Normal mode for display. 
• Examples using the WorldMap CD use the MapSource maps for N 30-40° W 70-80°.  These four files used 1026K.  This example is using the "More" mode.
• Examples using the GPS III Plus Base Map use the "Most" mode.

In an effort to try something new, I made the screen dumps in portrait mode.  Last time I do that!  It took me a couple of hours to rotate them from the output provided by G7TO.  Ouch!

This is the tightest zoom level.  There is probably an EPE circle, but you can't see it because the MapSource enabled GPS has colored the background as gray, indicating park land.  All devices have the overzoom indicator lit.  This indicates that the map is being displayed at a higher resolution than it's designed for and plotted objects such as roads and rivers are being extrapolated for display.  MapSource provides less granular data -- you can see this because of the Estimated Predicted Error (EPE) & Map Accuracy circle.  The display for the Topo shows the new "Tree" icons for parks and the driveway on the north side of the White House, as it's a landmark.  The circle is still off the display on the base version.  For comparison, the display off to the right shows the effect of EPE without Map Accuracy.  I turned off the base map and MapSource map on the III Plus to get this display.

U. S. Roads & Recreation					Topo	WorldMap	Base
Most	More	Normal	Less	Least	Normal	More

The diamond icons represent various areas of interest and are provided by MapSource.  In this case, most of them represent statues located in Lafayette Park!  WorldMap apparently does include some extra streets -- H street is not in the base map.  You can see the new icons here, including the church to the northeast.

The diamond to the northeast with the legend "SAI" is St. Matthew's Roman Catholic Church.  The full text is displayed if you place the pointer over the icon.

This is the first level where the MapSource enabled maps don't display overzoom.  Least mode is already starting to remove streets.  Note how U.S. 29 is a straight line on the Least mode, but curves on the other MapSource maps.  A contour line snakes north of the 500ft indicator to the east on the Topo map.

Less mode is starting to drop detail at this point and it's displaying the same information as least.  In the three most detailed screens, you can see an "H" in a circle.  It is the Washington Post building, I do not know if it has a Heliport as you might think.  The WorldMap mode is out of overzoom.

Normal mode has started to drop detail.  I think it's interesting that the three least detailed maps are exactly the same.  I would have thought that there might me somewhat more variability in the display.  WorldMap demonstrates that it does have a couple of more roads than the base map and it is correcting the contours.

Most & More are completely unusable at this point.  Check out the circle around the Lincoln Memorial on the WorldMap.  There are bridge icons at the south of the Topo map.

Finally More has dropped down a level.  Notice that Least mode is now displaying the same information as the base map, BUT IT DOES NOT HAVE THE OVERZOOM indicator lit!  It's an unfortunate problem, as the data is not accurate.  The data displayed on Topo is very similar to the Normal mode of R&R, but the large icons use much of the display.  Because of the sheer number of points of interest in DC, this probably isn't the best demo of the Topo map's features.  If I were to redo the other maps with revision 2.02 of the GPS III Plus software, they should have the same issues.

Top three levels are the same again.  The G on a black dot found to the south in the Potomac is a navigational aid.  If you point the arrow at it, it says "FL (2+1) G 6S".  Notice that the two least detailed levels are the same as the base map, but do not indicate overzoom.

The hatch marks to the southwest are Alexandria, Virginia, a separate MapSource map that I was not able to load.  The metro areas are fixed in version 2.02.  You can see that Alexandria, VA is a metro area now.

This is the lowest level where the base map does not overzoom.  Notice that the Least mode display now shows less detail than the base map.

You can clearly see the MapSource demarcation lines on the less detailed MapSource displays.

Only the Most detailed map is still using MapSource information.  The cross hatch lines that you're seeing on that map reflect that I have not loaded Charles County, Prince William County, Stafford County, Farquier County to the south and Anne Arundel County & Howard County to the northeast.  WorldMap also uses MapSource information -- check out the navaids at the bottom of the display.

No display uses MapSource at this resolution, and the Most detailed and the base map have the same display.  You can see an icon for Dulles airport to the far west.  Check out the 30 mi. display and higher on the WorldMap.!  The crosshatch pattern indicates an area where maps aren't loaded.  The WorldMap data is still being used as you can see very subtle differences (like the roads around York, PA), but I wonder if it's worthwhile for the WorldMap data to be used at this resolution?  Answering my own question, I guess so -- if we were mapping in Europe, we would need the WorldMap data for coastlines to at least the 200 mile zoom, and for cities and roads all the way out to 500 mile zoom.  The maximum zoom range for Topo is 12 miles, but because I used normal mode, it's not using MapSource data at this zoom.