Module 8 - Flow Mapping ....stylized distributive flow....I can go with that

This week’s module was an introduction into flow line mapping.  There are many types of flow maps, Distributive, Network, Radial, Continuous and telecommunications to name a few of the most used.   This lab, depicting immigration into the United States for the year 2007 is a type of distributive flow map.  We mapped the quantitative data found in the U. S. Homeland Security Office of Immigration Statistics 2007 Yearbook of immigration statistics.  Since we did not know the actual migratory paths, we used a stylized placement approach to represent the general direction of flow and indicated quantities through the use of proportional flow arrows.  The line weight of the flow arrows was calculated by taking the square root of the population value of each Continent; we then chose a maximum value line width, in this case 15.  With those two pieces of information we applied the following formula using the highest population value as our denominator, in this case Asia with 619.28 resulting in the following formula for each of our continents where X=continents square root population value: Width of line symbol=15*(X/619.28).  This calculation gave us a line weight for each continent that was proportional to the immigration value for that region.  This made it easy to draw conclusions regarding relative quantity of immigrants per continent. 

Critical to the use of low maps is figure ground.  The flow lines should be the most important element in the visual hierarchy.  I made these a dark color which was separate from any other color on the map, applied appropriate proportional symbology and experimented with stylization effects to find one that provided additional visual hierarchy without being overpowering or distracting; my final choice was a subtle drop shadow effect.  The topic of projection was already solved for us in this case, but none the less is an important decision when creating your flow map.  I had no issue with the provided continent color schemes or with the U.S. Choropleth map and, therefore, chose not to alter them.  I did increase the size of my map area to fill the paper as well as enlarge my inset choropleth map for additional clarity.  In both instances I was careful to group the scales with their associated maps so that they remained proportional.  I labeled the continents for clarity, added a title, author, date, source and projection information.  At this point I decided to apply a fill color to my background.  I used a blue tone that was slightly dark to not only represent the oceans, but to also make the continents and flow arrows stand out more.  I then turned my attention to the legend.  I used a contiguous color range legend for the choropleth inset map to show the percent of total immigrants per state.  I used a second legend for the main map to connect the immigration values by continent to the U.S.  I thought keeping with the “arrow” theme would be attractive; consequently, I created a series of arrows that gradually reduced themselves in length as the quantity of immigrants decreased.  I match the colors of these arrows to their continents and, since I had made them wide enough, included the continent name and immigration value inside each arrow.