This section criticize bad or not so bad maps or interactive visualizations.
It is often worth looking and learn from bad design, as the Cartastrophe website suggests.
The Deepwater Horizon oil spill (also referred to as the Gulf of Mexico oil spill) was an oil spill that began in April 2010 in the Gulf of Mexico on the BP-operated Macondo Prospect, considered the largest accidental marine oil spill in the history of the petroleum industry. Following the explosion and sinking of the Deepwater Horizon oil rig, which claimed 11 lives, a sea-floor oil gusher flowed for 87 days, until it was capped on 15 July 2010. The total discharge is estimated at 4.9 million barrels.
This map was made by the NOAA Office of Response and Restoration.The interest aspect of the map is that is wonderfully illustrate the point we are stressing here. That the communication channel can be disrupted at three different levels: operational (perception), articulatory and/or semantic. Each of these level here is undermined by this example.
Operational distance (perception).
The choice of colors and how they are placed definitely is not optimal. The main reason is because of the confusion of the overlapping of colors. Users' eyes cannot perceive effectively between the different colors that are stacked in partly transparent polygons. This means that the “region tracking” is not efficient as it takes time to try to locate the zones (if you can).
This representation might be effective when two or three colors are overlapped but not with six colors. It's already hard for the user to separate six various colors as the limit of the human eyes is situated around seven landings of different grey tints.
Moreover the poor contrast between some colors, such as April30 and May3, doesn't help the user to distinguish well the periods. The chosen colors are not the same and are flashy : the first day is blue and the second is blue-green, then the autor use all of a sudden orange-red and yellow colors to finish with green and orange colors. I think it would have been best to use the saturation of one color to represent each days and the expension of the oil slick. PLus, why is one part of the ocean blue and the other white ? And the blue is lightly different then the blue used for April 28 which is confusing.
After observing the map that should describe how the oil slick has progressed during a week, we can see some details that are not well explained in the legendary. The map doesn't makes use of a cleaver legend to convey information :
Thanks god, the autor didn't forget the distance scale that is a big need in this map as with it we can see how big is the oil slick and how much it's expanding.
The map was made to show the week evolution of the oil slick from the explosion. This shows why stacked, partly transparent polygons are a poor choice to show a multi-day event as we can't clearly see that the oil slick is enlarging and gets closer to the coast. The autor message was to inform people that the winds would cause a slow transport of the oil slick towards the coast.
What should be done.
Nowadays, in order to give users a feeling for how the situation changes from day-to-day, the best is to show it with an animated map that evolve in live. The best representation of the oil slick was made by the New York Times that created an simply and amazing animated map which contains relevant data (habitats affected, states affected, fishery closures, and benchmarked estimates of the spill size).
The New York Times map : http://www.nytimes.com/interactive/2010/05/01/us/20100501-oil-spill-tracker.html
The map is simple, and we can clearly detect the boundary and track the different regions of oil slick each day. There is no colors confused or overlapped. A well-made map.