A1-RobinHeld
From CS294-10 Visualization Fa07
Contents |
[edit] Good Example of Visualization:
[edit] Explanation
The image to the right was taken from A Brief History of Time, by Stephen Hawking. The pair of figures were used to illustrate the concept of 4-dimensional space-time, and how multiple past events lead up to a single event in question, which in turn influences many future events. He writes, "If one thinks of a three-dimensional model consisting of the two-dimensional surface of a pond and the one dimension of time, the expanding circles of ripples will mark out a cone whose tip is at the place and time at which the stone hit the water (Fig. 2.3). Similarly, light spreading out from an event forms a three-dimensional cone in the four-dimensional space-time. This cone is called the future light cone of an event. In the same way we can draw another cone, called the past light cone, which is the set of events from which a pulse of light is able to reach the given event (Fig. 2.4)." Put another way, one could imagine an analogy to a family tree that includes both the ancestors and the descendants of a single person. As you go back through the generations, the number of ancestors increases exponentially (to a degree). Assuming the person and his/her descendants reproduce at some minimum rate, then the number of descendants increases rapidly with each generation, as well. Hawking makes the point that events have similar cause-and-effect relationships with each other.
[edit] Deconstruction
The visualization consists of two figures. Both include three quantitative axes. Two of the axes are devoted to space, while the third (vertical) axis is assigned to time. Here, time is the independent variable. The top figure illustrates the expanding ripple created by a stone hitting the surface of the pond. It includes what may be considered ordinal image captures of the pattern of ripples, each of which employ the 2d space axes to illustrate the surface disturbance. Dashed lines are also overlaid to emphasize the cone of influence the stone splash exerts on the surface as time progresses. The second figure is more general, as it illustrates the influence of one generic event in space-time. In addition to showing the event's influence on future events, it also includes the "past light cone," which shows how the number of past events that affect the event in question increases as one goes back in time.
[edit] Critique
The pair of figures do an excellent job of leading the reader from a simple concept to a much more complex one. The example of ripples on a pond is something anyone can imagine and understand. Through analogy, it makes events in 4-d space time more comprehensible.
[edit] Bad Example of Visualization:
[edit] Explanation
The preceding image was taken from the Time Science Library book entitled, The Engineer. It was drawn to illustrate the original transatlantic telegraph cable laid in 1858, as well as its replacement line, which came in 1866. Specifically, its purpose was to show the terminal ends of the cables, as well as how they were moved between iterations.
[edit] Deconstruction
The image is a map, so the quantitative measures of latitude and longitude are employed. However, a universal scale of distance is lacking, as indicated by the severe compression of the Atlantic Ocean. This makes it difficult, if not impossible, to make any quantitative assessments based on latitudinal or longitudinal coordinates. The two cables are displayed as nominal variables. Both are drawn as dashed lines, with text labels differentiating them. Bodies of land are indicated by text labels, as well, though some important ones, such as "Newfoundland" and "Ireland" are omitted.
[edit] Critique
The map is jumbled and confusing to read. In particular, the geography the author chose to represent makes it difficult to visualize the overall paths of the lines. It shows a Northeast portion of Newfoundland on the left and a Western portion of Ireland on the right, but only the former is labeled. Without knowledge of the larger land masses to which the two sides belong, it is difficult to understand their locations on the globe. Additionally, the varying geometric scale is problematic. The Atlantic ocean is clearly scaled down significantly, making the overall scale of the image difficult to glean.
[edit] Redesign
It would have been far more useful to show the entire paths of the lines across the Atlantic, as well as zoomed-in images of the terminal ends. The redesigned figure below uses the juxtaposition of three images to convey both the local and global paths of the cables:
To create this image, I chose to only display the submerged portions of the cables. The original image also included the path of the cables as they snaked inland, but they were difficult to follow and not critical to the declared purpose of the figure. After doing some background research, I found that the cables did not terminate in any specific towns, so the endpoints are not labeled with location names. Comparing the redesign to the original, the first and second cables are also more clearly differentiated. Rather than relying entirely on text labels, the redesign uses different colors and dashed vs. solid lines to indicate which line is which. Also, the geometric scale is clearly labeled in each sub-map. I was slightly concerned that the reader may not immediately realize that the Ireland map and the Newfoundland map are on different scales, since both maps have the same dimensions on the screen. To emphasize the difference in scale, I made the cable lines heavier in the Ireland map.
Overall, the redesign is a succinct, clean representation of the paths of the first two transatlantic telegraph cables. The entire paths are clearly indicated, as well as the local geography of the terminations of the lines.
