Which Gestalt law states that human have tendency to group connected elements?

Proximity

Spatial proximity is a powerful perceptual organizing principle and one of the most useful in design. Things that are close together are perceptually grouped together. Figure 6.2 shows two arrays of dots that illustrate the proximity principle. Only a small change in spacing causes us to change what is perceived from a set of rows, in Figure 6.2[a], to a set of columns, in Figure 6.2[b]. In Figure 6.2[c], the existence of two groups is perceptually inescapable. Proximity is not the only factor in predicting perceived groups. In Figure 6.3, the dot labeled x is perceived to be part of cluster a rather than cluster b, even though it is as close to the other points in cluster b as they are to each other. Slocum [1983] called this the spatial concentration principle; we perceptually group regions of similar element density. The application of the proximity law in display design is straightforward.

[G6.1] Place symbols and glyphs representing related information close together.

In addition to the perceptual organization benefit, there is also a perceptual efficiency to using proximity. Because we more readily pick up information close to the fovea, less time and effort will be spent in neural processing and eye movements if related information is spatially grouped.

Similarity

The shapes of individual pattern elements can also determine how they are grouped. Similar elements tend to be grouped together. In Figure 6.4[a, b] the similarity of the elements causes us to see rows more clearly. In terms of perception theory, the concept of similarity has been largely superseded. The channel theory and the concepts of integral and separable dimensions provide much more detailed analysis and better support for design decisions. Two different ways of visually separating row and column information are shown in Figure 6.4[c] and [d]. In Figure 6.4[c], integral color and grayscale coding is used. In Figure 6.4[d], green is used to delineate rows and texture is used to delineate columns. Color and texture are separate channels, and the result is a pattern that can be more readily visually segmented either by rows or by columns. This technique can be useful if we are designing so that users can easily attend to either one pattern or the other.

[G6.2] When designing a grid layout of a data set, consider coding rows and/or columns using low-level visual channel properties, such as color and texture.

Connectedness

Palmer and Rock [1994] argued that connectedness is a fundamental Gestalt organizing principle that the Gestalt psychologists overlooked. The demonstrations in Figure 6.5 show that connectedness can be a more powerful grouping principle than proximity, color, size, or shape. Connecting different graphical objects by lines is a very powerful way of expressing that there is some relationship between them. Indeed, this is fundamental to the node–link diagram, one of the most common methods of representing relationships between concepts.

[G6.3] To show relationships between entities, consider linking graphical representations of data objects using lines or ribbons of color.

Continuity

The Gestalt principle of continuity states that we are more likely to construct visual entities out of visual elements that are smooth and continuous, rather than ones that contain abrupt changes in direction. [See Figure 6.6.] The principle of good continuity can be applied to the problem of drawing diagrams consisting of networks of nodes and the links between them. It should be easier to identify the sources and destinations of connecting lines if they are smooth and continuous. This point is illustrated in Figure 6.7.

Symmetry

Symmetry can provide a powerful organizing principle. The symmetrically arranged pairs of lines in Figure 6.8 are perceived more strongly as forming a visual whole than the pair of parallel lines. A possible application of symmetry is in tasks in which data analysts are looking for similarities between two different sets of time-series data. It may be easier to perceive similarities if these time series are arranged using vertical symmetry, as shown in Figure 6.9, rather than using the more conventional parallel plots.

To take advantage of symmetry the important patterns must be small. Research by Dakin and Herbert [1998] suggests that we are most sensitive to symmetrical patterns that are small, less than 1 degree in width and 2 degrees in height, and centered around the fovea. The display on the right in Figure 6.9 is far too large to be optimal from this point of view.

We more readily perceive symmetries about vertical and horizontal axes, as shown in Figure 6.10[a, b]; however, this bias can be altered with a frame of reference provided by a larger-scale pattern, as shown in Figure 6.10[c] and [d]. See Beck et al. [2005].

[G6.4] Consider using symmetry to make pattern comparisons easier, but be sure that the patterns to be compared are small in terms of visual angle [