For the 2017 solar eclipse, NASA published eclipse maps that took the irregular umbral shadow of the moon into account: the umbra is neither circular nor oval but irregular—more polygonal—thanks to the uneven topography and elevation of both the moon and the earth. Not accounting for that introduces errors into the map that could make the difference between observing a partial rather than a total eclipse. The process behind those more accurate eclipse maps, which involves computer processing of both lunar and terrestrial elevation models, has now been published in The Astrophysical Journal. [Bad Astronomy]
Dr Root and colleagues from TU Delft and Utrecht University used tiny deviations in the orbits of satellites to investigate the gravity field of Mars and find clues about the planet’s internal mass distribution. This data was fed into models that use new observations from NASA’s Insight mission on the thickness and flexibility of the martian crust, as well as the dynamics of the planet’s mantle and deep interior, to create a global density map of Mars.
The density map shows that the northern polar features are approximately 300-400 kg/m3 denser than their surroundings. However, the study also revealed new insights into the structures underlying the huge volcanic region of Tharsis Rise, which includes the colossal volcano, Olympus Mons.
If the road grid in online maps of China doesn’t line up with the aerial/satellite imagery layer, Anastasia Bizyayeva explains in a Medium post earlier this year, it’s because China’s map data uses a different geodetic datum, GCJ-02, rather than WGS-84. “GCJ-02 is based on WGS-84, but with a deliberate obfuscation algorithm applied to it. The effect of this is that there are random offsets added to both latitude and longitude, ranging from as little as 50m to as much as 500m.” Chinese map companies are obliged to use GCJ-02 so their maps and imagery line up; outside China, companies can choose to use Chinese data and imagery and have alignment artifacts at the Chinese border, or use Chinese data with images aligned with WGS-84 and have the roads appear offset from the imagery. [Kottke]
Most of the maps in the Atlas of Iowa, which came out last month from University of Iowa Press, are thematic maps: mainly graduated symbol maps and (to a lesser extent) choropleth maps, that show data at the county or (to a lesser extent) census district or precinct level. These are functional maps, means to an end rather than impressive examples of cartography in their own right. They do the job they were designed to do, which is to present the history, demographics and economics of America’s 29th state in cartographic form. And by and large they succeed: I’ve never so much as set foot in Iowa, but the Atlas of Iowa taught me a great deal about it.
The U.N. has launched an online Atlas of Ungulate Migration. “Driven by tracking data on ungulate migrations, the Atlas of Ungulate Migration serves as a repository for up-to-date migration maps that can inform conservation planning, infrastructure development and policy making. The maps detail high, medium and low-use migration corridors for a diversity of species, ranging from the iconic Serengeti wildebeest and African elephant, to the saiga of the Central Asian steppe. Most importantly, the maps illustrate where critical migration routes intersect with linear barriers like roads or railways. This atlas represents the best available science for extant migrations, with downloadable maps each accompanied by a factsheet describing the migration in detail, the data analysis, and its specific threats. The atlas is living, and continually updated.” News release.
Some coverage of two map books published earlier this year by Bodleian Library. First, Atlas Obscura interviews Kris Butler, whose Drink Maps in Victorian Britain looks at how the temperance movement used maps to fight excessive alcohol consumption. They were, apparently, directly inspired by John Snow’s cholera map. From the interview:
Drink maps were specific to targeting the U.K. magistrates, to try to get these lawmakers to stop granting licenses. So it had a really specific legislative, regulatory goal. […] In one case [in 1882, in the borough of Over Darwen in Lancashire, England], after looking at a drink map, the magistrates decided to close half of the places to buy alcohol. Their rationale was, even if we close half of these, you still don’t have to walk more than two minutes to buy another beer, which I just think is the most beautiful rationale I’ve ever read. It was challenged, and it held up on appeal.
Meanwhile, the Bodleian’s own Map Room Blog (no relation) points to Debbie Hall’s Adventures in Maps, a book about maps and travel and exploration. From the book listing: “The twenty intriguing journeys and routes featured in this book range from distances of a few miles to great adventures across land, sea, air and space. Some describe the route that a traveller followed, some are the results of exploration and others were made to show future travellers the way to go, accompanied by useful and sometimes very beautiful maps.” I reviewed Debbie Hall’s Treasures from the Map Room (also no relation) in 2016.
In the long history of mapmaking, computers are a relatively new development. In some ways, computers have fundamentally changed how cartographers create, interpret, and share spatial data; in others, they simply mark a new chapter in how people have always processed the world. This exhibition features objects from the Leventhal Center’s unique collections in the history of digital mapping to explore how computers and cartographers changed one another, particularly since the 1960s. By comparing maps made with computers to those made before and without them, the exhibition invites us to recognize the impacts of digital mapping for environmental management, law and policy, navigation, national defense, social change, and much more. Visitors will be encouraged to consider how their own understanding of geography might be translated into the encodings and digital representations that are essential to processing place with a computer.
There’s more than one way to depict data on a map. At the last Esri user conference, Sarah Bell, Kenneth Field and John Nelson demonstrated different ways to map the results of the last U.K. parliamentary election, and how they changed from the previous election. The video of their presentation is attendee-only, but Ken and John have posted about how they each went about their tasks: here’s Ken’s post and here’s John’s; plus, as is his wont, John has posted a video.
Last month NASA Earth Observatory ran a two-part series about the Shuttle Radar Topography Mission, which produced a high-resolution digital elevation model of the Earth based on radar data collected by the shuttle Endeavour in 2000. The first part looks at how Endeavour gathered the data, the second part at how it’s been used.
Nearly a quarter century after the mission to map the world, the SRTM’s data still yields results. Just this year, it aided in wildfire forecasting for Iran’s Zagros Mountains, tracking soil erosion in South Africa, assessing flood risk on the coast of Brazil, and even determining how the locations of power-generating wind turbines affect real estate values. Tens of thousands of research papers are published every year that rely on SRTM maps for these and other environmental, economic, agricultural, and public safety studies.
