General:
The new TOPO 2008 maps are approximately $90 -check for latest discount prices (HERE).  These maps are constructed from DEM (Digital Elevation Model) data instead of a digitized version of the USGS 1:100,000 topo maps for the older USA Topo maps.  Contour lines from DEM data are interpolated between the elevation points, which can be 10m, 30m, 90m, or more, rectangular cells.  A very small part of the US is surveyed at 10m cells.  It appears that the new Garmin topo maps are using the 30m cells.  Using DEM data also lends itself to calculating shading.   To turn the shading ON or OFF in MapSource, go to: Edit, Preferences, Display.  (The shading isn't transferred to the unit).

The TOPO 2008 street data have fewer vectors than USA Topo, but the streets are named.  The street data appear to be from a late TIGER database.  Since the contour interval (in the Atlanta area)  has been reduced from 32 feet to 25 feet, there are more contour lines.  However, in the mountainous area of Oregon, the USA Topo maps actually have more contour lines than the Topo 2008 maps (see below)

There has been some discussion that the elevations of certain peaks have different values than other maps.  So far, we've not been able to determine which maps are more authoritative.   There also was hope that the segments would be larger, so the 2025 segment limit with many units would not be an issue for those wanting to load the complete map onto the new microSD cards which can hold up to 4GB.  (The 2008 topo maps have a total of 6633 segments.)

Usage:
The new topo map shading can be used to quickly evaluate a terrain of interest on a PC.  Also the more densely-spaced contour lines will be helpful for orienting one's self in a strange area.  The addition of street names will be helpful, but don't expect to see Garmin's usually accurate street placements as with the USA Topo maps.  The map doesn't autoroute, however selecting a GoTo will cause most units to autoroute on the base map.

Jack Yeazel