Flow Mapping

Hey there Mappers!

This week's focus is on Flow Mapping.  In particular, the map we created was a distributive flow map.  For those who don't know what a distributive flow map is, it depicts the movement of commodities, people, or ideas between geographic areas.  The map I created this week depicts the number of people who legally immigrated to the United States in 2007.  So how did I make this map?  Glad you asked because I am going to give you a basic run down on how I did this using Adobe Illustrator.

The first challenge was determining which provided template to use and how I would lay everything out.  Ultimately I chose Layout A, which had the world continents and an inset showing the immigration rate for each state.  From here I separated each continent (conveniently grouped in the template) and placed them around the artboard in Illustrator.  I then enlarged the "lower 48" states and moved Alaska and Hawaii closer to mainland USA.  One thing to note is that the scale bar was enlarged with the mainland to maintain proportions.  Next was fine tuning the positions of the continents around the United States.  With the main layout complete there was just one last piece that had to be added, that was for the "Unknown" immigrants.  For this I simply made a circle, placed it appropriately on the map and added a question mark to show that it was unknown.

The next big step that I worked on was placing the flow lines on the map using Illustrator's pen tool.  This allowed for nice arcs to depict the movement of people from a continent to the US.  This layer I placed below the continents layer, giving it a nice start point and then ending right before the US.  While the pen tool is a little wonky to get used to, it really can make nice flow lines on the map.  The next part for the flow lines was assigning the correct proportional width.  Using the data provided in excel, math was applied to determine the correct proportions based on a max width of 16pt.  Here is how my proportions came out:

• Africa – 8pt
• Asia – 16pt
• Europe – 9pt
• North America – 15pt
• Oceania – 2pt
• South America – 8pt
• Unknown – 1pt 

With the majority of the map laid out, all that was left was to add the essential map elements and stylize the map.  I created a legend for the Percent of Total Immigration per State by creating boxes and then using Illustrator's eye dropper tool to match the colors.  Then I added the appropriate labels throughout the map along with the essential text elements in the lower right corner.  Here are the stylize elements that I used on my map:

• Dark Background – I felt this contrasted best with the lighter colors of the provided continents
• Outer Glow – I applied this to the continents and immigration layers.  I felt this helped those elements pop out from the dark background.  One thing to note is that I had to duplicate my continents layer to apply the outer glow and place it lower on the precedence table as the glow was fading out my flow arrows in a way I did not like.  
• Drop Shadows – These were applied to the continents, the immigration map, title and flow arrows.  For the continents, there was a softer drop shadow which gives the overall map a more 3D look with the glow and dark background.  The continent shadow even covered the starting segments of the flow arrows which gave them a nice effect.  The title has a nice subtle drop shadow that doesn’t extend too much from it.  For the flow arrows I used a hard drop shadow which I felt helped to emphasize the point of the map, that being immigration to the United States.    
• Continent Colors – For the most part, these stayed stock to the provided .ai file.  However, I did recolor Africa as the colors for Asia, Africa, and Oceania were all similar and I wanted there to be some separation of continent colors.  
• Text Color – This was fairly simple.  I used black coloring against the lighter colors and white against the darker colors.

After all was said and done, I was left with the map below.  Let me know what you think!