It has been certified by the Guinness World Book of Records as the world's largest rotating globe, but snaring that designation was simply a side benefit of Maine mapmaker DeLorme's decision to create the 42-foot-diameter behemoth.
"It was just done as a challenge," said Jim Peterson, technical head of the company's core libraries.
The globe, nicknamed Eartha, fills a three-story glass atrium at DeLorme's headquarters in Yarmouth, in southern Maine. It conveys the physical geography of the world in typical fashion -- blue for water, tan for arid land, and green for fertile areas. But there is nothing typical about the globe's scale. At 1:1,000,000, one inch equals almost 16 miles. California is three and a half feet high. DeLorme lights the globe up at night, and it's so big that, viewed at 60 miles per hour from a nearby highway, it nonetheless looks just like what it is: a big glowing ball of a world.
Depicting physical geography at that scale required lots of highly detailed data. But while much of the world has been finely mapped, much has not. For example, data was sketchy for the Himalaya, many South American countries, and much of Africa, according to Peterson.
"Very often (data disparities start) on political boundaries, where one country had better surveying than the other," Peterson said.
The data disparities had to be smoothed out so they didn't give the globe an inconsistent appearance. In some places, DeLorme showed less detail than it could have, in order to eliminate stark contrasts between well-mapped areas and areas for which there was less data.
"It's one world -- we needed one look," Peterson said.
The ocean floor presented another challenge. For example, sea floor near the state of Washington was very finely mapped, thanks to a strong U.S. military presence in Seattle, but the nuances of much of the rest of the ocean floor are only broadly known, Peterson said. Ships' soundings provide reliable information, but soundings produce information only for those areas over which the ships pass. A given sounding map is also a map of that ship's course across the water. To fill in the spaces between ships' trips, DeLorme turned to David Sandwell of the Scripps Institution of Oceanography in California. Sandwell had used a radar altimeter aboard a satellite to measure the surface elevation of the ocean, which bulges or compresses slightly depending on whether the sea floor below is mountainous or low-lying.
DeLorme spent a year pulling together Sandwell's ocean depth data, or bathymetry, other data from satellite imagery, non-pictoral data from the company's databases, and shaded relief elevation data.
"When you combine all [the sources of data] you get something that has a punch to it," Peterson said.
The company wrote software -- a map engine -- to tie all the sources of data together, and the result was a 140G-byte database, around 214 CD-ROMs' worth, Peterson said. For crunching the numbers, DeLorme used 400MHz quad-processor PCs running Microsoft Corp.'s Windows NT, he said.
The data was then rendered on 792 panels which were printed from a big plotter and then affixed to the globe, though first the boundaries of each panel were checked, pixel by pixel, to ensure proper match up, Peterson said.
Another quality assurance check of the data was to render it in 3D and "fly" through it like a fighter plane in a computer game. In 3D, bad data was easily visible as a tall pointy spike in a mountain chain of lesser, rounded peaks.
"You'd be literally flying around the data in 3D and all of a sudden see this tower," Peterson said.
The map engine created to crunch the geographical data for the globe is now used to help produce a number of DeLorme's retail products. But the map engine's maiden task was to create Eartha, an aesthetic object rather than a utilitarian one.
"We were primarily interested in getting something pretty," Peterson said.