It’s difficult to teach cartography as an expert because there are fundamental concepts that one can easily forget to impart on the students, though this can be ameliorated somewhat by following a comprehensive guide to core knowledge areas such as The GIS&T Body of Knowledge*. Even so, there are certainly some concepts that nobody anticipates struggling with, teacher or student, that are unique to each project undertaken. To tackle these project-specific struggles the cartographer must possess a certain amount of patience, research prowess, and a passion for discovering new solutions through a willingness to test and revise.
It’s these project-specific issues that I haven’t written much about on this blog, instead focusing on fundamentals like typefaces, colors, and layout. Thinking about this hole in my writing, I decided to take notes while creating my most recent print map. Hopefully these notes can be instructive in not just detailing specific solutions to specific problems, but also in providing a more general picture of the types of things that come up in a typical cartography project.
These notes include ideas on skills employed, issues encountered, and paths not taken. Here is the map, in reduced resolution, because it is not considered a fully finished product just yet. The final version will be somewhere around 8-10″ on a side. The notes follow.
PROJECTION USA contiguous Albers equal area conic, an easy choice for the display of the contiguous U.S. and distances should be fairly accurate for the middle latitudes, which are inclusive of this data. This is important since I’m running some distance calculations and reporting on them in the layout, though of course I can always conduct the calculations separately from the display projection by simply starting a new GIS project with a different projection. In this case both needs are met with the one projection. So here I’m thinking, “does the projection look right? Does it calculate right (i.e., not distort the things I want to measure)?”
TRAIL DATA The trail line is a subset of linework from a university teaching database and I have not thoroughly explored its validity though comparisons by-eye to other maps of the journey show at least a superficial agreement. My need to trust this line is a problem. What if it’s wrong? How many times to cartographers blindly use data without complete knowledge of it’s correctness? In this case I’m helped by the fact that my partner in this project is a historian who can do some verification for me. In any case, verification of data should be a part of every cartographer’s workflow.
LINE RESOLUTION AND DISTANCE CALCULATIONS Another potential issue with the line trail data that crossed my mind was the issue where perhaps the line-digitizer made the line too “squiggly,” perhaps due to an unsteady hand (red line in the zoomed-in example below). If this were the case, then the distance calculations could show the Lewis & Clark crew going much greater distances than they really did. A worry, indeed, and next on my list of things to take a close look at. (Of course, conversely, distance calculations coming from a simplified line would under-report the true distance traveled.)
One section of the trail. The non-dashed black line is the real data, the dashed black line illustrates how distance would be too-low if calculated from a simplified line. The red line indicates distance would be too great if calculated from a line with inaccurate and artificially high numbers of vertices.
TERRAIN DISTANCE On a related note, the terrain distance can be much different from the straight-line distance for each segment. The straight-line distance over a ravine is shorter than the traveler’s distance, since they presumably hiked down and then back up the ravine on the other side. In the elevation profile, the true terrain distance is reported. This may account for the fact that my total mileage is greater than the total mileage reported elsewhere for this expedition.
LINE SPEED INSET: for this kind of visualization, sometimes we see the width of the line changing by speed but most often it’s depicted with a sequential color scheme instead. I’ve chosen to go with a pseduo-sequential color palette so that all the colors are clearly visible in the small space. The boldness of color needed for the size of the space is an interesting consideration that I haven’t written about before. In this inset, the expedition’s speed is calculated from a length field divided by a to/from date field converted to # of days per segment. This length field isn’t terrain-distance and thus could be a source of error. The inset still serves as a good at-a-glance comparison of the relative time it took the expedition to traverse each segment. The placement of the inset came from an inspiration map. Maintaining a rich library of inspiration maps is a must.
PAGE EFFECTS Who knew that you’d need to figure out how to create squiggly lines in Inkscape to evoke old parchment edges? Nobody, that’s one piece that can be learned on-the-fly. Also, get good at finding svg or raster textures to use as backgrounds, especially on these historic map styles. I’ve also seen lots of textures on contemporary map styles, usually in grided dot patterns. (Hint for the squiggly line page border: draw a rectangle and then use Filter>Filter Texture>Rough and Glossy and fine-tune the result with the Filter Editor as the Inkscape filters often default to startingly bold results.)
PROFILE GRAPH Exporting a profile graph is possible using a QGIS plugin called the Profile Tool. You can also create profile graphs with ArcMap’s Elevation Profile Add In. The tables of profile data that are produced for each segment of a given line can be exported to spreadsheet software to produce a nice looking graph (the graphs that are automatically output from these aren’t really suitable for a well designed map layout.) Using spreadsheet software (in my case, Excel) I made a graph, switched the progression to East–>West since that’s the direction they were headed, and further styled the graph in Inkscape. This was a process that probably took half a day or more from researching tools to implementation to styling. I even used a pen tool set to smoothing 25% to trace over the excel-derived profile line in order to create a more pleasing line (since my original profile had a point for every mile along the 4,000 mile route and created quite a jagged looking profile line.) Switching a profile graph’s direction to suit the data was a mental hurdle, overcome only by thinking, thinking, and more thinking about the data and the story I was trying to tell. This is something we’re always talking about: know your data, think about your story.
TYPEFACES The typefaces are chosen to complement the historic look of the map. Gabriola is used since there’s limited text and its decorative nature seems to suit the overall style. There are Myriad other fonts I probably could have used, and likely a better one will crop up as I revise. (The Myriad reference, ahem ahem, is a little type joke for the type nerds.)
X AXIS LABELS The x axis labels are problematic and will need to be redone. They depict distances at the segment end points, which is useful, but too jarring in the context of an x axis, which traditionally shows a smooth progression of numbers. An experiment gone awry. Sometimes, oftentimes, our experiments don’t work out. Note the axis lines and labels are in a medium-dark gray. I want them to remain firmly in the background as supporting information.
PROFILE LINE COLOR I considered changing the color of the profile line depending on the altitude. Green at low altitudes, progressing to brown, and finally white at the highest altitudes. A hypsometric tint for a profile chart! This seemed a bit much though, given the complexity of the rest of the page.
COLORS AND PRINTING The saturation of the hillshade will likely need to be adjusted once I see this printed on the final medium. It looks good on my screen but vast experience with this shows me that it can likely look too dark or too light depending on the press and the paper. Web designers have it easier in this respect. They’ll go on about how every monitor is different and that phones produce glare outside. But that’s nothing to needing a perfect print out on one media type and getting it wrong. There’s no excuses when it comes to printing a map in a known format (in this case, the map will be in a book so I will need to do a lot of exacting color proofing when the proofs come in.)
COASTLINE The overly stylistic coastline with drop-shadow was chosen specifically to comport with the historic style, though you’ll notice I didn’t interpret “historic” so literally so as to include such unfounded ornamentation as author cartouches or sea dragons. One must have boundaries. (Joke: boundaries, coastline, ahem.)
LET GO OF YOUR STYLING DARLINGS I am so hung-up on water=bright blue that when I began the map I of course made the water a very bold solid blue. It took several days of mulling over before I realized that was all wrong for this map. Pouring over the file of inspiration maps that I’ve been keeping for this project, it took only a few minutes to come up with an alternative to the blue, but only once I knew what I was looking for. This seems to be a frequent problem for cartographers who have a wide repertoire of map styles. They can intermingle to the great detriment of the final map unless time is taken to think things over. Knee-jerk styling such as my dark blue ocean (a modern map color for oceans) is only helpful if you keep to the same style-genre (e.g., historic, modern) all the time.
This wraps up my notes on the making of this map. Hopefully there will be a few bits you can use in your next project.
*The GIS&T Body of Knowledge is a great reference document when interviewing for a new GIS position. Use it as a check-list, checking off areas you have a firm understanding of and noting what subjects you need to study more.