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The number of lines in the closed paths in the drawing.

The degree to which lines in the drawing touch features of the photo that are difficult to perceive.

Whether or not the drawing contains optical illusions such as a line that appears curved.

The degree to which a given line in the drawing is suggested by the photo.

The degree to which it is believed that one who is gifted at spatial reasoning will consider the resulting two-part image to be interesting.

Ways in which the drawing may be interpreted as depicting an object that has broken into pieces that have moved apart.

The degree to which the drawing is different from other drawings in the series.

The degree to which the drawing contains (secondary) lines that touch, or are directly related to, features of the drawing rather than the photo. For example, a line that ends at the intersection of two other lines in the drawing, where the point of intersection is not a distinguishable point in the photo.

The number of lines in the drawing.

The number of horizontal lines in the drawing.

The degree to which the slope of lines in the drawing is different from the slope of obvious lines in the photo.

The degree to which things in or about the two-part image are thought to be nonobvious.

Relationships between the drawing and prime numbers.

The degree to which there are lines in the drawing that could be extended to meet, or nearly meet some prominent point in the drawing such as a point at the intersection of two other lines.

The ease with which one can imagine particular 3-dimensional interpretations of the drawing.

The number of vertical lines in the drawing.

Relationships between lines that end at or near the right side of the drawing and objects at or near the left side of the photo.

The number of lines in the drawing that touch a given object in the photo. And how this number varies from object to object.

The various ways in which lines may be paired in order to imagine different 3-dimensional interpretations of the drawing.

The degree to which the drawing symbolizes the photo.

The way the two-part image looks at various distances (e.g. 18 inches and 10 feet).

Ways in which lines or other repeated forms in the drawing may be interpreted as depicting the movement of an object (or objects) by a sequence of positions visited over time.

The way in which the collection of lines in the drawing is distributed over the photo.

The number of lines drawn to edges of the photo.

The degree to which all the unique objects in the photo are touched in some way by some line in the drawing.

The degree of prominence of any simple form or symbol (e.g. a roof, star, triangle, face, stick figure, alphabetic character or number) that is in the drawing or suggested by it.

The degree to which the drawing is considered to be in accord with the photo.

The number of lines in each connected subset of lines in the drawing.

The distance between adjacent non-intersecting lines in the drawing.

The number of bounded regions formed by the lines in the drawing.

The degree to which each of the different features of a given object in the photo is touched by at least one line in the drawing.

The degree to which things in or about the two-part image are thought to be ambiguous.

The number of lines drawn to corners of the photo.

The degree to which the drawing suggests some line (or lines) that are not in the drawing. For example, this might be the case if there are three or more prominent points in the drawing (such as an endpoint of a line or a point at the intersection of lines) that are collinear, or nearly so, but no such line has been drawn.

The number of lines drawn to a given edge of the photo.

The length of lines in the drawing in relation to the dimensions of the photo.

The ease with which one may imagine different 3-dimensional orientations for a given line in the drawing. For example, one endpoint of a line might be seen as being closer to the point of observation than the other, or vice versa.

The degree to which lines in the drawing are parallel or nearly parallel.

The number of lines drawn to a given corner of the photo.

Instances where lines in the drawing nearly intersect.

The type of objects in the photo from which, to which, along which and through which a given line is drawn. And the degree to which these objects are different.

Whether or not a given line in the drawing that is nearly horizontal, vertical or 45 degrees from horizontal, should be adjusted to be exactly horizontal, vertical or 45 degrees from horizontal, and vice versa; thus affecting the degree to which the line is jagged.

The number of segments or steps in a line in the drawing that is not horizontal, vertical or 45 degrees from horizontal. Here, steps and segments refer to elements of the jagged lines that result when lines are represented by a pattern of points on a rectangular grid (as is done on a computer monitor).

The degree to which lines in the drawing are perpendicular or nearly perpendicular.

The structure of the sequence of joint types (e.g. T's and V's) encountered in traversing a given path through the drawing.

The degree to which different lines in the drawing touch different collections of object types in the photo.

Paths formed by traversing a sequence of intersecting lines in the drawing. For example, a path might begin in the following way: traverse line 1 until line 2, which intersects line 1; traverse line 2 until line 3, which intersects line 2; and so on.

The length of a given line in the drawing in relation to other lines in the drawing.

The degree to which the drawing is thought to be interesting by itself.

The number of lines in the drawing that intersect or nearly intersect at a given point or in the neighborhood of a given point.

The number of disjoint sets of intersecting lines into which the drawing may be partitioned. More loosely, the number of connected subsets of lines.

Relationships between the number of lines in the drawing (or the number of bounded regions) and the content of the photo.

The size of angles formed by intersecting lines in the drawing.

The degree to which lines in the drawing touch ambiguous features of the photo. An example of an ambiguous feature would be a face-like pattern for which it cannot be determined whether the form is a person who was in the photographed scene, an illusion formed by objects in the scene, or the result of a double exposure. Another example would be an unidentifiable small white dot that might be a photographed object or point of light, a defect in the photo, or a dust particle on the surface of the photo.

The ease with which one may enumerate the points and objects in the photo that are touched by a given line in the drawing.

The ease with which one may mentally superimpose the drawing onto the photo.

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