Many Garmin devices come with a pre-installed basemap (worldwide or regional), and these range from only having major roads and little other detail, to slightly better ones that have a little more detail and even some DEM data (on some models).
However, they are all very limited and of no real use in urban areas (cities, towns, villages, etc.) and even worse when out in the countryside as they have almost no useful data in them.
Our TT HD Topo & Topo Pro maps are far more detailed than not only the pre-installed Garmin basemaps, but even the Garmin TopoActive maps.
You can see some screen shots on how they compare to our maps, here.