18th-Century Maps Reveal Florida’s Missing Coral Reefs

From McClenachen et al., “Ghost reefs: Nautical charts document large spatial scale of coral reef loss over 240 years,” Science Advances 3, no. 9 (6 Sept 2017). Creative Commons licence.

In the 1770s British surveyor George Gauld mapped the Florida Keys, taking careful note of the location and depth of Florida reefs. A study published last month in Science Advances compares Gauld’s maps with modern-day satellite imagery and concludes that half of the area occupied by coral in the eighteenth century has disappeared. As the Washington Post reports, the cause of the coral’s disappearance is unclear, though several potential human and natural factors are put forward. [WMS]

Maria’s Deluge

Some of the most striking maps of the recent bout of hurricanes have involved the sheer amount of water dropped by these storms. (See previous posts on Harvey and Irma.) Above, a is a short NASA video showing Maria’s track through the Caribbean, dumping water in its wake.

Relatedly, the Washington Post produced maps of precipitation and river gauge levels on Puerto Rico that show just how much water Maria threw at that island.

Washington Post

Tracking Hurricane Irma

Washington Post

As they did with Hurricane Harvey, both the New York Times and the Washington Post graphics departments have frequently updated map pages showing the projected path and impact of Hurricane Irma. The Times’ page looks at the hurricane’s current and projected path, threat of coastal flooding, and areas under evacuation, plus some context; the Post maps Irma’s forecasted path on this page and the potential storm surge and evacuation zones on this page, while this page compares Irma’s size to past hurricanes.

Mapping Hurricane Harvey’s Impact

Washington Post

The Washington Post maps rainfall and flooding levels in the Houston area.

The New York Times is collecting several maps on two web pages. The first page deals with subjects like rainfall, river level, current and historical hurricane tracks, damage reports, and cities and counties under evacuation orders. Maps on the second page look at Harvey’s impact on the Houston area.

Esri’s U.S. Flooding Public Information Map includes precipitation and flood warnings.

Kenneth Field critiques the National Weather Service’s decision to add more colours to their precipitation maps (see above). “Simply adding colours to the end of an already poor colour scheme and then making the class representing the largest magnitude the very lightest colour is weak symbology. But then, they’ve already used all the colours of the rainbow so they’re out of options!”

More Election Cartography Primers

nyt-foldout-map
The New York Times

Today, print subscribers to the New York Times were treated to a fold-out map showing a choropleth map of the 2012 election results at the ZIP code level (above). “The map is part of a special election section that aims to help explain the political geography of the United States — identifying where people who are conservative and liberal live and pointing out how physical boundaries, like the Rio Grande and the Cascade Mountains, often align with political ones,” writes the Times’s Alicia Parlapiano.

Parlapiano’s piece is in fact a lengthy tutorial on how to read election maps, along the lines of the pages I linked to in last week’s post on election map cartography—it outlines the problems of state-level election maps and choropleth maps that privilege area over population, for example, and shows some other ways of depicting the results.

It can’t be a coincidence that in today’s Washington Post we have Lazaro Gamio’s article dramatically highlighting the difference between area and population size with comparative maps. Mark Newman’s cartograms also make an appearance.

I can only conclude that both the Times and the Post are making efforts to educate their readers before the election results start coming in, one week from tonight. (Deep breath.)

Data Visualization’s ‘Dirty Little Secret’ and Choropleth Maps

The Washington Post’s Christopher Ingraham compares two choropleth maps of U.S. population growth: while they look rather different, they use the same data. “The difference between my map and Pew’s—again, they both use the exact same data set—underscores a bit of a dirty little secret in data journalism: Visualizing data is as much an art as a science. And seemingly tiny design decisions—where to set a color threshold, how many thresholds to set, etc.—can radically alter how numbers are displayed and perceived by readers.” [Andy Woodruff]

(Worth mentioning that this is exactly the sort of thing dealt with in Mark Monmonier’s How to Lie with Maps.)