Flow Maps

Creating flow maps using ArcGIS program

Visualizing the spatial patterns of ‘traffic volumes’ in the
Puget Sound Regions in Washington State from 2000 and 2030. Practice how to analyze traffic change over time, in particular with using flow maps
The significant volumes of traffic are weighted in the west side of the Puget Sound Region. Especially, the west side of King County, where the area of Seattle is, shows extreme amount of traffic volumes in the year of 2000. In the map B, which shows the difference of traffic volumes between the year of 2000 and 2030, we can see the major increment of the traffic volumes indicated with the color green. Most places where have great volumes in the map 2000 are anticipated to increase the volume of traffic in 2030. However, we can also see the significant reduction of traffic volumes near the center of Seattle area and noticeably increased volumes around the Seattle area especially to the east side where I-90 is and Tacoma area. This can mean that the traffic that were concentrated to the Seattle is expected to be more spread across the Puget Sound region.
Limitation of flow maps and design issues I encountered with regard to data symbolization
The Lines in flow maps show the number of volumes by changing the size of width of lines. In our assignment, flow maps deliver the message effectively which part of region has more or less volume of traffic compared to other areas in the Puget Sound Region. In addition, in the map that indicates the difference of traffic volumes between two years provides the information of not only the amount of volumes but also the increasing/decreasing of volumes by choosing different width with different color for each.
However, flow maps show their limitation on the map, especially when the size of map is not efficiently big enough to show the different sizes of widths of lines. Even though the size of map can be considered as a big enough size, readers can get confused when certain region has too much information with wide lines. In this case, readers cannot recognize the volumes of data, or even worse cannot recognize which road is connected to which road.
Thus, choosing the right range of width of the line to avoid this problems was important issue that I had to consider in depth. While avoiding that problem, we still need to show the difference of data in noticeable way. Therefore, balancing these two considerations was an important design choice to make a better flow map.
For the future, I think it would be beneficial to have different versions of this map. For instance, the current version might show great deal of detailed information, but at the same time, having too much information make the target information less visible. So, I think we can make different version of this map, which only shows the roads that have greater volume change over a certain threshold (ex. 3000), will make the map more useful, if the purpose of this map is to only to show the anticipated volume changes.

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