A biweekly tour of the ever-expanding cartographic landscape.

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Stock your bunkers: On April 6, a so-called “mini Y2K” is coming for GPS. The global positioning system operated by the U.S. government enters its third “epoch” on Saturday, entailing a numerical reset that could screw with older navigation devices.

Huh? Let’s back up. Your friend GPS—the infrastructure that pinpoints smartphones, cars, and watches, plus scientific instruments, banking systems, and electrical grids—is calibrated in large part based on time. Satellites beam signals down to earthly receivers, which capture the gap between the time of transmission and arrival. Quantifying that lag helps align the position of one receiver relative to others.

Without the correct timestamp, GPS instruments might get confused. (Giphy)

All of these times are measured based on a point in a sequence of numbers. Originally, the way GPS devices encoded the week was in a limited, 10-bit field. That meant that no more than 1,024 weeks (just under 20 years) could be handled by a receiver, periods that are known as GPS “epochs.” The first began on January 6, 1980, and the third begins on Saturday, which is when some older GPS devices would reset to week “0.” Eventually, they could start spitting out inaccurate timestamps. According to a slide deck about the epochal rollover by the U.S. Naval Observatory, “each nanosecond of relative satellite clock synchronization error can add one foot of ranging error.”

What does that mean for you? The GPS receivers embedded in most everyday consumer devices aren’t likely to be affected, since many newer devices use a 13-bit field that can handle much longer epochs. And a lot of GPS software can be updated remotely by manufacturers to weather the turnover. (In-vehicle navigation bigwigs Garmin and TomTom are confident that their customers won’t be affected, as they’ve already rolled out fixes.)

Zoom in, zoom out. (Giphy)

But the last epochal change did result in data failures, in many cases long after the 1999 pivot. Motorola, Novatel, and the USNO experienced breakdowns in some of their older receivers related to this problem in recent years, and it’s possible that this week’s turnover will produce more.

Scientists—everyone from seismologists to particle physicists—are girding for glitches too, Nature reported this week. Universities and consortiums are busily updating software systems, but some harder-to-replace instruments will inevitably fritz out, generating bad data that’ll take tedious effort to correct, just like in 1999. “We will still be on the edge of our seat during the rollover,” Brian Donahue, a senior geodetic engineer at Natural Resources Canada in Ottowa, told Nature.

For most of us, the great GPS reset won’t be the end of the world as we know it, much like Y2K. But it is a glimpse into the surprisingly fragile (and analog!) foundations of our very digital world.  


Audits hit the Black Belt

Just in time for tax season, here’s a grim picture of where and on whom the IRS performs the bulk of its audits. Drawing data from a report by former IRS economist Kim M. Bloomquist, new maps by ProPublica show that counties in the heavily African-American U.S. South, from Mississippi to Georgia, experience a much higher rate of auditing intensity than, say, the whiter upper Midwest and Northeast.

(ProPublica)

CityLab’s Brentin Mock reports on the maps:

The 10 counties with the highest IRS audit intensity are all found in the Black Belt, eight of them in Mississippi alone. Baker County’s 9.2 audit rate pales in comparison to Humphrey County, Mississippi, where the rate is about 11.8 audits per 1,000 filings. The Northeast region of the U.S. meanwhile appears to be largely protected from the IRS’s fine-tooth combs, despite the larger volume of wealthy households in that area.

Read more and interact: “Where in The U.S. Are You Most Likely to Be Audited by the IRS?” (ProPublica)


Mappy links

Looking north at a 1920s land-use map of Scotland’s Ochil Hills in a new 3-D viewer. (National Library of Scotland)

Curb, your enthusiasm: The hottest piece of location data in cities is where the sidewalk meets the street. (CityLab) ♦ Expanding the ride-hailing map: Uber is hustling to map the Middle East ahead of its IPO. (Reuters) ♦ Opposite of progress: Comparing the breadth of urban transit systems, today and yesterday. (Guardian) ♦ Extremely hot map porn: A trove of old maps from Scotland’s National Library can now be explored in a 3-D digital viewer. (National Library of Scotland)


MapLab: locating the future in maps. Sign up your friends and family.

Cheers,

Laura Bliss

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