PROOF
THE BACKSTORY
A CREATIVE MAPMAKER SHOWS THE MISSISSIPPI RIVER’S
HISTORICAL TWISTS AND TURNS.Lidar reveals Louisiana’s Wax Lake delta. Colors show elevation from dark (low) to light (high).FOR CARTOGRAPHERS and cartophiles,
Harold Fisk’s 1944 maps of the lower
Mississippi River are a seminal work.
In the mid-20th century the geologist
charted the river in stunning detail and
accuracy, using aerial photos and local
maps. The centerpiece of his report
was 15 maps showing the meandering
Mississippi and its historical flood-
plains stretching from Missouri to
southern Louisiana.
More than seven decades later,
Daniel Coe, a cartographer for the Wash-
ington Geological Survey, wanted to
re-create Fisk’s maps with greater accu-
racy and a new aesthetic. Coe had the
advantage of hyperprecise U.S. Geo-
logical Survey (USGS) data collected
using lidar, a system of laser pulses
sent from aircraft to measure topogra-
phy. The lasers detect the river’s shape
along with everything around it—every
house, tree, and road. Strip away theselayers of vegetation and human add-
ons, and Coe’s maps show the river’s
bare-ground geomorphology: once
lazy bends replaced by direct flow, old
floodplains cut off by levees and dikes.
USGS scientists collect lidar data
(almost all of it open-source) to visual-
ize how land evolves, and enterprising
mapmakers can interpret the data in
new ways. Slight changes in elevation
can be the difference between a peace-
ful river and a devastating flood. Exces-
sive soil runoff from agriculture can
cause river migration and create longer
shipping routes.
All of the above makes a river’s past
behavior the best indicator of how
it might react to future landslides,
floods, or erosion. “The most surpris-
ing thing is how much of an imprint
is still left on the landscape,” says Coe.
“It’s like seeing fingerprints the river
left behind.” —DANIEL STONE14 NATIONAL GEOGRAPHIC