It may be the signature color for the next generation of planetary topographic maps.
In addition to standard geologic maps, USGS also produces outreach maps of planets and moons. The last in this series is the Image Mosaic and Topographic map of the Moon, released in April 2015. Its press release reached 3.3 million viewers, and it has printed 5000 copies so far for distribution.
Trent Hare with the SIM3316 map at LPSC 2016
It’s not easy to describe what colors it uses. Starting from deep ultramarine blues (for the deepest craters and maria), it becomes royal blue and then light blue (for most of the maria), reaching white around 2000 m of elevation, where lava plains give way to the densely cratered highlands. So far it is not dissimilar to the traditional cartographic colors of depths. Then, instead of moving to warmer colors, it remains neutral and darkens until reaching black, at 10,780 m.
This map appears to use only one color: different shades of blue for “depths”, and grayscale for “heights”. And it can still work to show you both small details and the lunar topographic dichotomy (with the aid of the shaded relief), probably even better as if it used all the colors of the rainbow.
Looking closer, however, it turns out that the grays of the highlands are in fact browns, with a pinch of yellow in the gray. But this is more evident on the printed map than on the screen. At least on my screen, they look just grey.
Looking even closer, the only color, blue, isn’t one color, either. For a Russian eye, dark blue and light blue are definitely two distinct colors with two different words for them: goluboy, for light blue and siniy, for dark blue. To sum up, its color scheme is tricky, complicated and still looks so simple.
It wasn’t designed to be like this. Trent Hare, a cartographer at USGS says that he prepared several different color variants that were put on display in the office hallway and left there for more than a month. As the colors ripened, most certainly mentally, they were also checked for by color blind people. The early test versions included rainbow color schemes well known from the MOLA Mars maps. To finally narrow down the selection, his colleagues voted for their preferred version – and, somewhat to his surprise, the blue-gray version won.
Blue-white-brown color schemes do exist in different varieties built into GIS applications, so it is not at all impossible that it will be used in the future for displaying MOLA data as well.
The map displays only a handful of place names. They were selected for their significance in lunar geology, not solely by the size of the feature. The map also shows the lowest and highest points on the Moon, first determined by the Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) instrument, which provided the topographic data for the maps. This map is, in fact, a twin, the other being an LRO Wide Angle Camera (WAC) photomosaic.
The WAC albdeo map shows more names, but still just the most important ones, and the locations of landing sites – using a turquoise green color.
Planetary Color Schemes
The fist decade of the 2000s was the decade of Rainbow Mars, released by the MOLA team in 1999, made similarly from laser altimetry data. It is ubiquitous in research papers, simply because most topographic maps products of Mars are pre-colored (for example in Google Mars) that can’t be changed. This rainbow color scheme has received many critiques, but still widely used, because scientists believe that if we use ALL possible colors, it would show the most details a human eye can possibly see. But for research purposes, scientists use the original data, and for the map product, simplicity and attractiveness may be more important than minuet details. (In addition, research shows that rainbow maps can be easily misinterpreted.)
The missing ingredient
Cartographers often say that cartography is made up of three major ingredients: science, technology and art (aesthetics), serving the same purpose. Cartography is far more than choosing the right projection. In planetary maps, the professional aesthetic control is often left out of the equation. Those maps, produced by the scientists themselves and not by cartographers, are more like multilayer displays of geospatial datasets than maps. Scientific investigations in astrogeology still rely heavily on maps, more than ever, but instead of making grand end products, these maps are visual summaries of geospatial datasets that will serve as raw products for further research, perhaps just a building block, a layer in someone else’s GIS.
This year, the word “Cartography” was removed from the name of the strategic body in planetary cartography (founded as the Lunar Photography and Cartography Committee in 1974), as dynamic geospatial data systems are getting more importance than cartographic end products. This re-established body is now called “Mapping and Planetary Spatial Infrastructure Team” (MAPSIT). Luckily, however, USGS still strives to maintain classical cartography techniques that includes creativity, user testing and meticulous control of symbology and linework. Trent Hare et al.’s map is an excellent model for what our planetary maps should look like. Simple, accurate and yet aesthetically pleasing. Even non-cartographer MAPSIT uses it as a profile image on its website as a telling indication that aesthetics and cartography still matter.