Using the same broad outline of the Campo in Siena from two posts ago, I’ve overlaid the sketch with a diagram of the important points that I visualized in the scene—the extent of my view, the relative position of the Torre del Mangia, and the foreshortening of the Palazzo Pubblico.

To further illustrate the phenomenon of foreshortening, I’m using a plan diagram of the Campo to show where I stood as I sketched and my angle of view. You can compare the actual width of the Palazzo Pubblico, shown with the white arrow, with my foreshortened view of it, shown with the black arrow, and notice its position relative to the horizontal sweep of the Campo space.

You can also see, both in plan and in the perspective sketch, the positioning of the Torre about one-third of the way across from the right-hand edge of the view. I visualized diagonals to estimate the height of the Torre relative to the width of the space.

While these are necessarily optical judgments, not precise measurements, seeing these types of relationships and imagining them on the page as you set up a drawing on location are important steps in the process.

Foreshortening is the apparent change in form an object undergoes as it rotates away from our point of view. This phenomenon is usually seen as a contraction in size or length in the direction of depth, the amount of contraction depending on the degree of rotation. The more a line or plane is rotated away from our point of view, the greater its apparent contraction. You can easily see this as a door opens away from you. Gauging and drawing the phenomenon of foreshortening can be a bugaboo for sketchers because our mind can persuade us to draw what we know—the actual size or length of something—rather than how that thing might appear to the eye—its apparent size or length.

To illustrate a case of foreshortening I want to use this view of the Virginia V that I sketched this past Sunday before the Seattle UrbanSketchers group met at the Museum of History and Industry for its January meeting. One of the reasons for gathering at MOHAI is the beautiful exhibit there of Gabi Campanario’s impressive work documenting the life and times of Seattle over the past six years for the Seattle Times.

The Virginia V, built in 1921 by Anderson & Company and launched in 1922, was part of the mosquito fleet that plied the Puget Sound waters largely between the First and Second World Wars. After WWII, the Virginia V changed hands several times as it served as an excursion vessel. It was placed on the National Registry of Historic Sites in 1973. Completely refurbished by the Steamer Virginia V Foundation, the Virginia V is now anchored at the south end of Lake Union and continues to be used for public excursions and private charters.

In this view of the same Virginia V sketch, I’ve overlaid some markers to show the relationships that I gauged and used to control the foreshortening of the ship. The most important step is ensuring that the apparent length—from the prow on the left to where the hull curves away from our view on the right—is correctly foreshortened relative to the height of the prow. Then, I positioned elements, such as the wheelhouse and bridge, relative to the left and right extents. Note how I try to suggest the way the hull is curved from fore to aft. You can use the span of your hand, the shaft of your pen or pencil, or any similar means to gauge these measurements but it is an essential step in the process. Otherwise, your mind will strongly suggest that you should draw what you know rather than how it appears to the eye.

When an architect, designer, or builder says that a building has “good bones,” this generally means that it is well built. Like others, however, I would extend the meaning of the phrase to include not just the sturdiness of a construction but also the soundness of its underlying organization and layout. A design with good bones should be able to endure flaws in workmanship or execution and gracefully accept the changes made to improve it.

So it is also with a sketch. To begin a drawing done on location, we must first select an advantageous viewpoint that conveys a sense of place and frame the composition to fit on the page. Then, a crucial step is establishing the “bones” of the drawing—its basic structure—with the first lines we draw. I like to say that the number of lines is five but this, of course, is arbitrary. For some views only a few lines may be necessary while for others, more might be required to establish the structure of a drawing.

It is essential to understand that once this structure is established, changes can still be made to calibrate scale, improve proportional relationships, and adjust the positioning of elements. Drawing these first few lines is simply a way to block out the essential relationships on a page quickly, before expending too much time on a drawing only to find out that a portion might be misplaced or is out of proportion to the rest of the composition.

Here is an example—a very quick outline of a view of the Campo in Siena that I did as a demonstration. With more time and better weather, I might have finished it but I think it is possible to see and visualize the space even in this incomplete state.