Blog for A Data Visualization Course at Columbia University
* Assignment #2 [zip]
* In-class mini-lab #3 [zip]
Tagged: Cartography, Data Visualization, homework, lab, maps
In the article “Value-by-alpha maps: An alternative technique to the cartogram” the author introduced an alternative visual equalization technique to the cartogram termed value-by-alpha mapping. They first mentioned the limitation of the cartogram/value-by-area maps which is a trade off among the three dimension: shape preservation, typology preservation, and visual equalization. Value-by-alpha, on the other hand, can solve the problem. It “concurrently can achieve perfect shape preservation, topology preservation, and visual equalization”, and is more straight forward. It is also mentioned by the authors that since value-by-alpha maps is still new, there is more to explore and with its own limitation, we cannot consider it as a replacement of the cartogram.
Comments on: Map Design—Borden D. Dent Cartography-Thematic Map Design, 5th ed. Chapter 13
The optimum solution for a map, which is said to be something not achievable by the author, could be approximated by applying several rules of design in different levels. The basic assumption for the success by applying those rules is stated by the author as: “more than one map element can be placed on a particular level, but a single element should never be assigned to more than one level (pp.2)”.
Three elements, balance, focus of attention and intraparallel organization are the three aspects of planar visual organization. Firstly, designers should do visualization according to some psychological rules. An image does not only have a geometric center but also an optical center, which is generally not far above the geometric center and could psychologically make people feel comfortable. Also, the famous designer Surrey says that “the reader’s eye normally follows a path from upper left to lower right in the visual field and passes through the optical center (pp. 5)”. Other than the relative location, shapes, colors as well as directions and subject matter also determine the relative perceptive importance of elements in a graph. “Golden Section” which though applied flexibly in different graphs, is empirically an almost indispensible strategy for good visualization. It could signify the relative importance of objects if their sizes and balances (the relative distances between objects or between objects and borders) are designed according to it. Generally, compared to the strategy of equality, improving the variety of visualization could generally improve the perception of viewers including leading to less reading difficulty and better memory of the map’s messages. Furthermore, for the map design, line contrast is an important method to strengthen or strike the balance and aids the reader’s perceptive focus. Other auxiliary methods like texture contrast, value contrast, variation of details and colors are also frequently used in map design.
The author spends the least words in the most important rule for the cartographic design in his work— hierarchy and figure and ground organization. Figures are generally the things that designer want to emphasis which should easily be captured by human eyes with the contrast of background. This design could only be determined after a sort through all of the components of a map and ranking the relative intellectual importance of each and thus, further contributes to the visual hierarchy of each component in a whole graph.
I am really curious about the last part since it does not tell anything like the methods to incorporate the design in each levels and the consideration of hierarchy. My concern is that the distances between adjacent levels are sometime not equal; there are probably one most important level, and several less importance levels that are distant from the most important one by do not differ a lot among themselves. Also, there are several non-important levels. If I could call it a “non-linearity problem”, what I need now is a rank of power of different elements since I could not only use shapes and colors which are entropy increasing elements on the condition that there are too many levels. Even if I had that rank and dedicatedly had applied those elements to different levels according to their different intellectual degrees, it seems that the construction of hierarchy in my case is easy only for the most important thing. An appropriate example is the campus map of Columbia University: the Low Library and the grassland are the most important landmarks. However, most people turning to the map probably want to locate a building for their class. Thought, people could always make sense of the relative location of their destination and the Low Library, it is hard for designer to actually assist them to find their destinations since he could not assign elements according to the number of classrooms or the specialties of majors to each building.
By Guangyu Tong
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