- Qinyu Ding
An Informal Heuristic Evaluation of NHC Tropical Cyclone Track Forecast Cone
Updated: Sep 24, 2019
The past two weeks were super crazy for me. The first week I was driven crazy by the preparation and waiting for Hurricane Dorian - as someone like me who had never ever experienced a direct hurricane before. My mind kind of went blank when I was feeling I was all set for Dorian. I was just sitting in front of my window, staring at that beautiful sunshine out there while checking Twitter for information of Dorian.
The second week I was addicted in reading parpers about visualization of Hurricane and uncertainty, which also drove me crazy, but in a good way. Part of the reason was because this was one of my assignment. But it was also because I had been obsessive with finding how designs frustrated/misled people. (Call me a geek as you like.)
I ended up doing an informal heuristic evaluation of NHC tropical cyclone track forecast cone which will be presented in the rest of the blog. PLEASE, feel free to make critiques on it.
METHODS
The heuristics/principles I used as references were Zuk and Carpendale’s Selection of perceptual and cognitive heuristics and Gestalt Principles.
Ensure visual variable has sufficient length
Preserve data to graphic dimensionality
Put the most data in the least space
Provide multiple levels of detail
Remove the extraneous (ink)
Consider Gestalt Laws
Integrate text wherever relevant
Don’t expect a reading order from color
Color perception varies with size of colored item
Local contrast affects color & gray perception
Consider people with color blindness
Preattentive benefits increase with field of view
Quantitative assessment requires position or size variation
PROBLEMS FOUND
The problem of the Note
Problem: The “Note” on the top of the graph is not obvious enough
The content of the Note includes some essential information about uncertainty and how to read this graph. However, with white text in black background, the contrast cannot easily catch the audience’s attention especially in a graph like this which contains a lot of information.
Also, long sentences tend to make people lose their focus while reading it. The audience are more likely to shift their focus to the cone before finishing reading the note, thus leading to significant misinterpretations of the graph.
My Recommendation:
Highlight the text in red and put it in a white background so that it provides strong contrast to draw attention.
Highlight the keywords by capitalizing them.
Communicate the content in short bulletins so that people do not lose their focus before finish reading it. And it is also easier for them to keep in mind. For example:
“1. It contains all the PROBABLE PATH of the storm center (with a chance of 60-70%)
2. The cone does NOT show the size of the storm.
3. Hazardous conditions can occur OUTSIDE OF THE CONE.”
Problems about the cone
Problem 1: The enclosed area can be easily misinterpreted as areas under effect
A general perception of an enclosed shape on a map is an area with the same attribute – for example, in this graph, people can easily interpret the enclosed cone as an area that WILL be affected by the storm.
Path, which is the correct interpretation of the graph, is a dynamic description consisting of several static descriptions which are different forecast positions. Thus, an enclosed area of a shape can be misleading.
Problem 2: Those dots can be easily perceived as a solid line indicating the track of the center of the storm
According to Gestalt’s Principle, people see the whole first as they automatically fill in gaps between elements to perceive a complete image [Closure (Reification)] . Therefore, the audience may connect the dots together and perceive it as a line representing the track of the center of the storm.
Also, Gestalt’s Principle indicates that people differentiate elements that are similar in color, form, pattern, etc. from others and cluster them together [Good Form]. Because the cone and the dots are different in shape and amount, it is easy for the audience to interpret them differently: cone = area under impact while dots = the track of the storm.
Problem 3: The enclosed cone fails to convey the rest 1/3 possibilities of the cyclone’s path
Even if it has been clarified in the Note on the top that the cone only represents 2/3 possible paths of the storm in the following five days. The solid border still gives people an impression of the boundary between area under impact and area free from impact.
Problem 4: The solid area and the stippled area can be misinterpreted as the intensity of the storm.
The solid area looking darker than the stippled area can make people think that areas covered by the solid cone may be affected by the storm more seriously than that covered by the stippled area. Again, time is a dynamic description while the cone shape is more likely to be interpreted as a static description which is the area under impact.
References:
https://www.nhc.noaa.gov/refresh/graphics_at5+shtml/205152.shtml?cone
CONE OF UNCERTAINTY SOCIAL AND BEHAVIORAL SCIENCE RESEARCH https://www.aoml.noaa.gov/general/lib/lib1/nhclib/Bibliographies/Cone%20of%20Uncertainty%20Literature%20Review_4_10_19%20%281%29%20%281%29.pdf
T. Zuk and M. S. T. Carpendale. Theoretical Analysis of Uncertainty Visualizations. In Proc. SPIE & IS&T Conf. Electronic Imaging, Vol. 6060: Visualization and Data Analysis 2006, 2006. 606007.
(n.d.). What are Gestalt Principles? Retrieved from https://www.interaction-design.org/literature/topics/gestalt-principles