This is the second in a series of short essays by Jeff Blossom, Chief Cartographer of the Out of Eden Walk. Jeff will periodically offer an inside view of the project’s map creation process by highlighting different mapping challenges and solutions.
Cartographic challenge: Mapping Ancient Exposed Seabeds on a Global Scale Solution: Leveraging a Human Legacy of Mapping
Our species has been making maps as far back as recorded evidence exists. Whether they be etched on a mammoth tusk, inked on parchment, or rendered on a smartphone, we’ve used maps to communicate where things are and to help us understand why events happen as they do. Two thousand years ago, Claudius Ptolemy understood the importance of recording and mapping our world — spurring him to write Geographia, in which he records latitude, longitude coordinates of about 8,000 then-known locations.
As nations expanded, so did their own geographic information collections, with the understanding that mapping one’s territory was often the best way to establish it, and certainly the best way to understand it: the topography, population, vegetation, water resources, and so on. With the information boom we are currently experiencing, there now exist datasets such as the Global Database of Events, Language, and Tone — a geo-referenced catalog of human societal behavior, beliefs, events, and more — which is updated daily and contains a quarter-billion recordings spanning back to 1979, all available for download by hungry cartographers to create maps and visualizations with.
The cumulative effect of humans recording details about our world in usable geographic format is a treasure trove for modern map makers. When faced with the challenge of depicting ancient seabeds globally, I turned to this trove of data, specifically NOAA’s ETOPO Global Relief Model. This data includes integrated land elevation and seafloor depth measurements, at roughly a one-kilometer spacing, covering the entire Earth.
Using ArcGIS mapping software from ESRI, it was a pretty straightforward task to render all land elevations using a shaded relief technique and apply a solid light gray color to all seafloors less than 120 meters deep (estimates of how much lower sea level was 60,000 years ago when humans began their migration vary, and we settled on 120 m). Then white was applied to seafloors deeper than 120 m. Here’s a snippet of the result:
This gargantuan human mapping effort continues and has escalated with technology, driven both by governments and public efforts such as OpenStreetMap that allow anyone to use — and even contribute — mapped data for free. I have a hunch Ptolemy would agree this is an extraordinarily exciting time to be a cartographer.