GPS vs. GPSMAP or Chartplotter
I'm not sure what you expected that is not there. This is a basic navigation aid. This type GPS will assist you when travelling from point A to point B. It assumes you create "waypoints" (destinations) from map coordinates that you have. String together a couple of waypoints and you have a route.
The typical automotive GPS units have map sets loaded in the unit and display route (navigation) data in map format.
If you want an on-water navigation unit that displays route information in a map format, then you want a unit that is part of the Garmin GPSMAP product line. An example would be the Garmin GPSMAP 76 Waterproof Handheld GPS.
A Chartplotter is a "big brother" to the handheld GPSMAP units. Additional functions at an additional price.
`99 Beneteau Oceanis 352, #282 WiTCHCRAFT
Sailing Lake Michigan and the Great Lakes