The cartographic considerations for our watershed map

For today's post, I'm going to have Will Edmunds discuss some of the decisions he had to make when creating his map of average monthly runoff for the major watersheds in the conterminous United States. As a reminder, Will is a Senior at Salisbury University, majoring in Geography with a focused track in Geographic Information Science.

The following are Will's observations:

This map was the most time-consuming project I’ve worked on to date. It was a

surprisingly difficult task to represent the watershed data in a visually appealing manner. The main issue I faced when creating this map was fitting the 18 separate runoff bar graphs on one layout, with all the information being legible.

I started off by bringing in the watersheds layer to get a feel for the proportion. I then brought in each runoff bar graph, to get their initial locations mocked up. It took a couple hours of resizing and rearranging to get the bar graphs to all fit on

the layout properly.

The bar graphs started off as basic Excel outputs, which I eventually color-

matched to each watershed, changed the fonts and styling, and removed the background fill.

Removing the background was a difficult choice, on one hand it greatly improved the look of the map, but they lost some legibility due to the terrain behind them.

For the leader lines, I opted for four equal angles, using horizontal and vertical segments to reach each watershed’s respective bar graph. I did this because having leader lines run directly from each watershed to their bar graphs was visually overwhelming and disorganized. This was very time-consuming, but that

alone vastly improved the overall look.

I streamed in a high-resolution topographic layer from Esri, brought in a USGS water

layer and open-source shapefiles for Canada and Mexico. I attempted to use a locally stored topographic dataset, but it was far too memory intensive for the computer I had access to. To mask the regions outside the US, Canada and Mexico in the topographic layer, I created a polygon around the northern hemisphere and clipped these regions out of it, since I could not run any geoprocessing on the topography layer.

For the watershed’s colors, I wanted to keep a natural color scheme, but also have distinct differences between each region, so I went with a green and blue color pallet and used the four-color theorem. I added a gradient fill and transparency to the watersheds layer and played around with the line thickness to add a depth effect to the watersheds. I ended up having the same effect on the Great Lakes, which turned out quite nicely.

For the rivers and streams, I found that many were too small to show up when the map was completely zoomed out as it would be on the layout. To combat this, I made a minimum line thickness of 1 point, losing some realism, but it made the map much more detailed. I brought in a state outline layer to provide context for the locations of each watershed.

For the title and map description fonts, I went through quite literally every font in Esri’s

database, until I was happy with what I had. My philosophy for this project ended up being “less is more”.

• The watershed colors all follow a somewhat pastel color pallet.

• The Pacific and Atlantic oceans are omitted from the map.

• Mexico and Canada are only given a topographical representation, to show that the land extends past the map’s extent but doesn’t pull focus.

• Even with the bar graphs, less was more with removing the backgrounds.

I wanted to see how beautiful a map could I create, with the cleanest possible overall look. This map was a serious challenge, but I’m quite happy with the outcome, and it was a fun learning experience.