GIS3015 Module 10 Lab: Flow Line Mapping

Mapping with flow lines provides a very simple graphic illustration of geographical movement of some phenomena. In this module a flow map was created to show the origins of and number of persons coming from other regions and obtaining legal permanent United States resident status. A choropleth map of the United States was created to show the percentage of immigrants to each of the fifty states. The graphic representations were based on fiscal year 2007 statistics obtained from the US Department of Homeland Security. Flow lines on flow maps must be hand drawn due to their individual and unique nature. Because of this, Adobe Illustrator was used exclusively to create the flow map.

preliminary sketch - horizontal

Far more than any other map created to date, this flow map took the most preparation to determine the best layout before even starting Adobe Illustrator. First in the process was sketching out two possibilities ~ a horizontal format and a vertical format, each one showing the location of the continents with flow line placement, location of the choropleth map and the legend. For each map a list of pros and cons was also created. The horizontal format allowed plenty of room to place the US in the center with the regions placed around the US with large flow lines directed to it. The horizontal layout seemed less busy, was very clear, and required shorter flow lines. The cons of the horizontal layout were that the regions were not viewed in their normal relationships to each other, and the map was very US-centric giving the impression that the US is of greater importance than the rest of the world. Although the purpose and focus of the map is to show immigration to the US from all other regions, the US-centric format was rejected eventually. On the other hand, the vertical format kept the US and the other regions of the world in their proper relationships, and the US was kept at the same scale as the other countries. 

preliminary sketch - vertical

Negative aspects of this format were that the flow line showing immigration from other parts of North America to the US was split and had to be joined near the arrowhead, and either the South American flow line had to cross the flow line coming from the region of Mexico/Central America or it would have to be placed in the already congested area of the east coast. That would be dealt with later, as this still seemed like the better layout choice.

The next step in the flow map-making process was to print out a preliminary layout for a working sketch. This involved placing the world map and choropleth map in an AI document and printing it out.

working sketch

Questions, notes, ideas, RGB colors for matching purposes, additions/deletions, and information that came up in discussion board postings as well as the flow lines were marked on this map or the initial hand-drawn sketch. This provided a way to keep all the necessary information and lab requirements organized and to minimize the possibility of leaving information out unintentionally. It was also a way to think out different ways of presenting the information prior to committing to making changes in Illustrator. With flow lines sized proportionally and matching the regions by color, the resultant map provides an easy to interpret comparison of immigration from different regions of the world. For specific immigration numbers, viewers can consult the chart included in the map. Ideally this chart would have included the color and size of flow line attributed to each region, but time constraints and other obligations precluded that this time.

Persons Obtaining Legal Permanent
U.S. Resident Status (By Region of Birth, FY 2007)

Choropleth colors were chosen to match the color of North America in the flow map. Normally the bar scale for a map would be placed lower than the legend of the map, but in this particular case it was placed closer to the map for ease of use. The orange color scheme of the choropleth map and the legend along with the size of the rectangles in the legend attract one’s attention directly to the legend from the choropleth map, so it still appears to rank higher visually if not physically.

While some aspects of using AI are becoming familiar, there is so much more to learn. Creating the flow lines was extremely difficult with each one requiring several attempts. Applying some of the special effects to the flow lines changed either the color, length or position of the flow lines with the longer lines impacted more severely than shorter lines. Because of this, only drop shadow was applied to the lines, and that had to be adjusted where the lines come together at the east coast of the US. Some workarounds for the other issues may be discovered with more practice. Throughout this map-making exercise, numerous copies of the map were saved at different stages to provide backup in case a special effect could not be undone for some reason. This exercise exemplified the extensive capabilities of Adobe Illustrator for creating or enhancing maps.