Here are the lines of the first boat I ever loved
There will never be another first love...
The uppermost view (profile plan) shows the sheer (top line) and the buttocks (which curve down from the sheerline fore and aft)
And of course the profile of the hull
(including the stem, canoe body and keel)
The upper half-breadth view shows the waterlines (and an edge-on view of the section locations)
while the lower half-breadth view shows the diagonals, and there's also the curve of sectional (underwater) areas - the one which meets the centreline at the ends of the waterplane - this last curve is the only one which does not define the 'lines' of the yacht, in other words, the shape of the surface.