This artist used line very creatively by using the shoreline to draw your eye to the bridge which in turn draws your eye straight the city. He used this natural lines to guide you through the painting.
Although this piece doesn't have boundaries the lines still add depth and the appearance of objects while keeping you focused on the subject matter.
Scipio Africanus Freeing Massiva, Giovanni Battista Tiepolo, 1719-1721 (Baroque), From the collection of: The Walters Art Museum
In this piece the lines play as a guide. The stairs form a mental line that leads you you to the man in the middle as do the structures in the back. From there the mans outreached arm makes a line that leads you to the other subjects in the painting.
This painting has a strong use of line to make a very realistic perspective view of this town street.
The lines in this painting are the subject matter. The lake is essentially just a thick line that stands out more than anything else. The clouds in the sky form a line around the moon explaining whats going on in the picture.