Garmin has several MapSource products, but this page highlights the first three -- U.S. Roads & Recreation, Topographic & World.  This page lists the features in common and unique to each product.  I have a matrix which compares the three products lower on the page.

• United States Roads & Recreation, which provides U.S. detail to the 500 ft. zoom resolution.  This data takes lots of space and is generally uploaded by counties.  Very large counties may be split in half to allow for some small bit of added flexibility in uploading.  The maps for the Dallas/Ft. Worth area, for example, completely fill the GPS III Plus.  The product is delivered on one CD.  Major features include:
  • Features
    • Interstates & highways, local/county/residential roads for all fifty states.
    • Points of Interest such as parks, camp sites, helipads, monuments and more.  Updates existing information on U.S. Interstate exit facilities.
    • Inland cartography with shoreline detail of lakes, reservoirs, rivers, boat ramps, dams, marinas, public facilities, mile markers, first aid & more.
    • Some U.S. nautical navigation aids of day beacons, radio beacons, RACONS, fog signals, lights, buoys and other navaids.  The inland navaids appear to be comprehensive, but the costal navaids are not.  They appear to be included on the Topo & WorldMap CD, though.
  • Applications
    • Probably the most popular MapSource product.  It's got complete road information along with plenty of information about parks and off-road areas.  It's probably also suitable for the casual outdoors user.

• United States Topographic, which provides U.S. detail to the 500 ft. zoom resolution.  This data takes lots of space and is generally uploaded by 1/2 degree segments.  Areas highly detailed areas will be uploaded by 1/4 degree segments.  The product is delivered on three CDs -- US East, West & Alaska/Hawaii.  The downloaded files are somewhat larger than the US R&R files.  Major features include:
  • Features
    • Similar to United States Geological Survey 1:100,000 scale topographic paper maps.  Includes elevation contours, point elevations, some bathymetric contours (some parts of the country have coastal underwater contours and some do not -- this is apparently because the data is not consistently available from the Government).
    • Interstates & highways, local/county/residential roads for all fifty states.  Does not include street names for local roads.
    • Points of Interest such as parks, camp sites, helipads, monuments and more. 
    • Landmarks such as oil fields, radio towers, runways, power lines & more.
    • Inland cartography with shoreline detail of lakes, reservoirs, rivers, boat ramps, dams, marinas, public facilities, mile markers, first aid & more.
    • U.S. coastal and inland nautical navigation aids such as day beacons, radio beacons, RACONS, fog signals, lights, buoys and other navaids.  The open water navaids are more complete than the U.S. Roads & Recreation CD.
    • Wrecks and obstructions such as: ship wrecks, submerged rocks, obstructions and other hazards to nautical navigation.
  • Applications
    • Has almost all of the features of the U.S. R&R product, and adds Topo features.  Serious outdoors users will prefer this to the U.S. R&R.  The significant things missing from this are local road names and Interstate exit facilities.
• WorldMap, which provides world-wide detail to the 800 ft. zoom resolution.  This data is less comprehensive than the U. S. Roads & Recreation CD.  In general it provides somewhat higher coverage than the International version of the Garmin GPS III (but I do not own one and can't tell you quantitatively how much more).  The data is uploaded in five degree grids which are highly variable in file size.  The New York to Boston corridor is a 1080K file, for example, but the file which includes almost all of the UK is 469K and some remote areas are easily in the 5K to 40K range.  The product is delivered on one CD.  Major features include:
  • Features
    • Base map level detail with worldwide coverage.  Outside of the Americas, the GPS III Plus map detail is only accurate to the 200 mi. zoom resolution.  If you zoom in closer than that, the base map will be extrapolated.  With a file from this CD loaded, you can zoom in to the 800 ft. zoom resolution.  This includes the Americas, where zoom is improved from 3 mi. to 800 ft.
    • Displays political boundaries, cities, towns, major Interstates & highways, lakes, major streams & rivers, urban areas & railroads.  In the Americas, little new detail is added, maybe 25% more streets along with lakes & rivers, but the zoom resolution is improved on existing roads.
    • Excellent coastline detail including many offshore islands.  I can confirm that many out-of-the way islands that I was looking for were on the map, including Wake Island, which included the appropriate navigational aids.
    • Worldwide nautical navigation aids of day beacons, radio beacons, RACONS, fog signals, lights, buoys and other navaids.  There do not appear to be any inland navaids, but the open water navaids are more complete than the U.S. Roads & Recreation CD.
    • Updates existing information on U.S. Interstate exit facilities.
  • Applications
    • Mariners will want this for excellent coastlines and the complete coastal Marine navaid database.
    • World travelers will enjoy having some international detail when they leave the Americas.  since the resolution is so high, you can't fit all that much of the world in the GPS at one time, but it will be suitable for many applications.  The product is an inexpensive way to approximate teh features of the International GPS III Plus (not yet available).

MapSource CD Features Comparison

		R&R	Topo	World
	Estimated List Price	$100	$130	$70
	US Coverage to 500ft Zoom
	Worldwide Coverage to 800ft Zoom
Transportation
	Major Highways
	US Interstate Exits & Services
	Local Roads
	Local Road Names
	Tunnels
	Bridges
	Airports
	Runways
	Heliports
	Railroads
Park & Recreation Areas
	National & State Parks
	National Forests
	Park Headquarters
	Hiking Trails
	Snowmobile Trails
	Campgrounds
	Boat Ramps
	Dams
	Marinas
	Public Facilities
	Mile Markers
	First Aid
	Picnic Areas
	Parking
	Swimming
	Skiing Areas
	Scenic Areas
	Beaches
	Fuel
	Danger Areas
	Restricted Areas
Topographic Features & Landmarks
	Elevation Contours
	Point Elevations
	Summits
	Some Bathymetric Contours
	Land Cover (Parks, Wetlands)
	Radio Towers
	Oil Fields
	Pipelines
	Mines
	Power Lines
	Geographic Names
	Ghost Towns
	Churches
	Cemeteries
	Schools
Water Features
	Lakes
	Reservoirs
	Small Bodies of Water
	Waterways
	Rivers
	Streams
Marine Navigation Aids
	Note: R&R Has Incomplete Set Of Coastal Navaids
	Radio Beacons
	Racons
	Fog Signals
	River Lights
	Harbor Lights
	Other Lights
	Lighted Buoys
	Daybeacons
	Unlighted Buoys
	Ship Wrecks
	Submerged Rocks
	Obstructions
	Other Hazards to Nautical Navigation.