Intervals are the spaces between points. An accurate eye correctly sees not only singular points and intervals, but ever larger groups of them. Therefore, as you improve your eye’s accuracy for specifics, you should also seek to increase your ability to accurately see in larger segments. This is part of what is called, seeing the whole.
To better understand this concept, take a look at the image above. In it you see that I have placed red dots at the positions where the outline makes a major directional change. These are called salient points. In some cases the choice was a bit subjective and I could also have chosen additional points.
The image below simply shows those points, connected by straight lines. You might recognize this as a block-in and it is how many artists begin a drawing. The key here is that all those points have a relationship to each other. That relationship is both horizontal and vertical. To create an accurate drawing of the arm, you would need to accurately position all of those points and they should read as true, as a whole.
In the later stages of drawing you would want to visually trace your eye along the entire upper contour of the source, numerous times. You would then do the same on your drawing. Comparing the two visual tracings should reveal any differences between the source and your drawing. During this process your eye sees both the points and the intervals (the spacing between the points). Due to your visual working memory, you see the differences when you switch your focus over to your drawing.
In the next image I have removed the line so that you can only see the intervals and the points.
Let’s see if you can correctly place the points in their proper intervals by eye. First, download the exercise sheets, here, and print them. Then, using some tracing paper, trace the bottom image on the first page, including the bounding box (the box provides your eye with some context). Also, trace the first point, along with every other point. There is no need to make the points as large as I have in the examples.
Next, using only your eye and visual triangulation, try to accurately plot the remaining points.
As you do this, pay attention to not only the distances between the known points on each side of your target point, but also to the next set of points. You want to try to think about the larger picture, not simply the smaller one of point-to-point.
Connect the points with lines, as you see on the second image above.
Finally, quickly trace your eye along the line on the source image. Begin at one end and follow the points to the other end. Then, jump back to the beginning and visually trace once again. Do this a half dozen times. When done, do the same routine on your drawing. Correct any errors you see.
When you think you are finished, go ahead and check your results by placing the tracing over the source image.
That was simply a warm-up exercise, but let’s try it again. This time only trace the first, fourth, seventh and last points, along with the bounding box. When you are finished tracing, rotate the tracing and the source by 90° so that it is vertically oriented. Then place the remaining points using just your eye following the same procedure I outlined above. Check your results when finished.
The farther away the points are from each other, and from the border, the more difficult it will be for your eye to accurately place them. Therefore, the first warm-up was likely a bit easier than the second.
On the remaining two pages of the download I provide eight more examples of this exercise – four horizontals and four verticals. To do them, use the directions from the preceding two warm-ups. You will therefore do each of the provided examples in two ways: the first with more given points and the second with fewer given points.
Accurately complete these 4×2 sets, even if it takes you a few times for each. After you succeed, you might create a number of your own examples, only make yours larger than mine. If you are using an 8 1/2″ x 11″ sheet of paper, draw two boxes which combined fill the page. Then, randomly place your dots within them. This will further test your eye since distance (a larger box size and point relationships) will make it more difficult.
This article is an edited selection from my book, An Accurate Eye | Learn to Draw Better by Learning to See Better.