1. Pacific Great Circle Routes Distance Analysis
This analysis is a collaboration between the Aleutian and Bering Sea Islands Landscape Conservation Cooperative, the Wildlife Conservation Society, and the Scenarios Network for Alaska Planning (SNAP) at the University of Alaska Fairbanks.

2. Study Area
The study area includes the Aleutian archipelago from Attu Island in the west to Unimak Pass in the east.

3. Gridded Data
Working with a set of gridded data produced by Martin Robards (WCS) and Michael Lindgren (SNAP)…

4. Idealized Routes
We identified three vessel transits that can serve as proxies for the majority of traffic along the North Pacific GCR. We refer to these as “idealized routes.”

5. Idealized Route Points
Each of the three idealized routes are broken down into a series of points, spaced at quarter degrees of longitude.

6. Idealized Route Chords
We then ran an analysis of distance to the nearest island from each point along the three idealized routes to create “chords.”

7. Idealized Route 1
Beginning with Route 1, we plotted a histogram of distance to nearest island by longitude to create a histogram. The horizontal reference line is 75nm, and we can see that the closest approach to islands occurs in Unimak Pass, which is not surprising. As the route moves to the west, it exceeds 75nm around longitude 170 degrees west in the vicinity of the Islands of Four Mounains. It remains at a distance greater than 75nm all the way to longitude 175 degrees east, at Buldir Pass. In the western Aleutians, the closest approach is to the north side of Attu Island at a distance of around 50nm.

8. Idealized Route 2
Idealized Route 2 is generally closer than Route 1, and while it exceeds 75nm distance at roughly the same point north of the Islands of Four Mountains, it is much closer to the Near Islands in the west. The minimum distance from this route to Attu Island is around 11nm.

9. Idealized Route 3
Idealized Route 3 is the closest to the archipelago, barely exceeding the 75nm distance in the central Aleutians. And to the west, it passes roughly 8 miles from Buldir Islands and 12 miles from the southeaster tip of Agattu Island.

10. Idealized Route 3
Idealized Route 4 which passes entirely south of the Aleutian archipelago is almost a perfect inverse of the first three routes. Here you can see that the distances to Attu, Buldir, and Unimak Pass are all greater than 75nm, and it’s the route passes close to the central Aleutians. The closest approach occurs in the Delarof Islands at about 10 nm.

11. Idealized Route Comparison