Hi @Anonymous
There are some differences in both lines, these are:
Model lines: You can use model lines to represent 3D geometry in a building design, the model line will be visible in the 3D view and all the plan views. You can sketch straight, curved, arc, circular, fillet, and tangent lines. (Compare with detail line and symbolic line.) Model lines are also used to create the 2D shapes used to create family geometry.
Simbolic lines: A line that provides information but is not intended to represent actual geometry in an element.
For example, when creating a door family, you might sketch symbolic lines in an elevation view to represent a door swing. Symbolic lines are visible parallel to the view in which you sketch them.
You can control the visibility of symbolic lines on cut instances. You can also control the visibility of symbolic lines based on the detail level of the view.
