How do ships safely navigate the San Francisco Bay? In his latest data viz roundup, Max Galka gives a guided tour of the Bay’s marine traffic, tracks trees in major cities, and maps the US based on the flow of its commuters

How do ships safely navigate in and out of the San Francisco Bay? This animated story map by Sam Kronick of Mapbox answers this question by taking you on a guided tour of the Bay’s marine traffic.

Based on 24 hours of telemetry data from the US Coast Guard, the map displays in striking detail the paths taken by every ship to sail within the Bay harbour on 1 September 2014. Each ship is categorised by size, and the depth of the Bay waters are conveyed using colour, adding some context for interpreting the ships’ movements.

For a fuller understanding of the various navigation patterns the sidebar guides you through the map. The story begins with the ships’ approach, as they line up in designated traffic lanes to avoid collisions. Once they reach the shallow waters just outside the Golden Gate Bridge, larger ships must rendezvous with one of the Bay’s designated bar pilots – experts in the area’s navigational hazards who help guide the ships into the bay.

Once inside, large cargo ships join a flurry of activity from smaller boats: high-speed ferries transporting passengers, private pleasure boats, and tourist ferries shuttling sightseers to Alcatraz or underneath the Golden Gate Bridge.

The clock in the upper-right corner of the map shows the time, and you can rotate its hands to watch the movement of the Bay’s marine traffic throughout the day.

Facebook Twitter Pinterest Treepedia: mapping the green canopy in cities. Photograph: MIT Senseable City Lab

Treepedia: urban street tree canopies compared

Aside from the beauty and character they add to a city’s streets, trees offer a range of social and economic benefits. By blocking the sun’s rays and increasing the rate of water evaporation, trees help mitigate extreme temperatures. Trees also absorb pollution, improving a city’s air quality. And their root systems make the ground more absorbent, reducing the risk of storm surges and floods.

In honour of street trees around the world, MIT Senseable City Lab has created Treepedia, a visual catalogue of the urban tree canopy in 16 global cities. Using the map, users can zoom in and explore each city to the level of individual trees.

Treepedia also allows you to compare cities and neighbourhoods by their Green View Index, a rating that measures the percentage of canopy coverage at a given location. The index accounts for the density of trees, and by analysing panoramas from Google Street View, it considers how buildings and other obstructions affect how the trees are perceived at ground level.

Facebook Twitter Pinterest The US divided into ‘functional megaregions’. Photograph: Garrett Dash Nelson/Alasdair Rae

America’s megaregions

A study published in the open access journal Plos One, has taken a novel approach to an old geographic problem: how to divide space into coherent unit areas. Rather than look at the US as a collection of 50 states, the study takes an empirical approach to the problem, partitioning the country based on the flow of commuters.



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The authors, Garrett Dash Nelson and Alasdair Rae, geographers from Dartmouth College and the University of Sheffield, base their analysis on a dataset of more than 4 million commuter journeys. Using a combined computational-visual approach, they divide the country into “functional megaregions”, arguably the real units that comprise the US economy.

To see what these megaregions look like when borders are applied, have a look at the full study – it’s worth a read for the striking visuals alone.

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