The San Juan Islands, located in the northwest corner of Washington State, form an archipelago comprising over 170 named islands and reefs. Although only approximately 20 of these islands are inhabited, the tourism industry of the four largest islands (San Juan Island, Orcas Island, Lopez Island, and Shaw Island) plays a vital role in the county's economy.

At the highest point within the island chain stands Mount Constitution on Orcas Island, reaching a height of 2,409 feet. A stone tower, constructed in the 1930s by the Civilian Conservation Corps, crowns its peak. The captivating vistas from this vantage point are often touted as a compelling reason to visit. One webpage from the San Juan Islands visitors bureau website entices visitors with descriptions of “360-degree views of the San Juan Islands, Vancouver, and the mainland, bracketed by snow-tipped Mt. Baker and Mt. Rainier,” while another emphasizes “panoramic views of surrounding islands, the Cascade Mountains and a variety of Canadian and American cities.”

Indeed, an awe-inspiring view can serve as a powerful incentive for travelers to navigate the ferry schedules and reach these geographically isolated islands. It can also serve as a rewarding experience after undertaking the challenging, steep multi-mile hike to the summit. However, it is essential to investigate the accuracy of these marketing claims. How much can truly be observed from this particular viewpoint?

The San Juan Islands visitors bureau is classified as a non-profit, 501(c) economic development agency and has functioned as the county's contracted, locally staffed destination marketing organization since 2003. They operate in partnership with the chambers of commerce and visitor information centers across the islands. Their marketing efforts directly influences the number of tourists who choose to visit and contribute to the islands local seasonal economy.

The Revised Code of Washington includes provisions regarding criminal offenses pertaining to false, misleading, or deceptive advertising (RCW 9.04.050). While the specific legal text is available through the provided link, in essence, it prohibits the deliberate display of known false information with the intention of inducing individuals to spend money on a product or service. Violation of this law carries penalties of up to five thousand dollars in fines, a maximum of ninety days imprisonment, or both.

Although these penalties may not appear overly severe, they could have significant ramifications for a non-profit organization. Therefore, it is crucial to substantiate any advertised claims in order to maintain good faith and preempt any potential legal issues in the future.

Process

The Shuttle Radar Topography Mission (SRTM) was a mission conducted in February 2000 using the Space Shuttle Endeavour to map the Earth's surface. Initially, data outside the United States was released at a resolution of 3 arc-seconds, which is roughly equivalent to 90 meters per pixel. In 2014, the data was re-released at a resolution of 1 arc-second, or 30 meters per pixel.

Using the USGS Earth Explorer website, I was able to download a series of 1 arc-second Digital Elevation Model (DEM) products from the SRTM that cover the northwestern part of Washington state and the southwestern portion of British Columbia. Using these void-filled TIF files as our source data provide consistent high-resolution elevation data across the national boundaries.

In ArcGIS, the Viewshed tool requires a single DEM as its input raster. To combine the collection of SRTM files into a single raster, I utilized the Mosaic to New Raster tool. Aside from selecting the appropriate input rasters, the most important setting to configure is the pixel bit depth, which was set to match the 16-bit pixel depth of the original files. As a bonus of the mosaic process, the stretched symbology gradient will be corrected across the entire region, instead of the unique minimum and maximum elevation values for each individual file.

The lookout tower's roof peak stands approximately 55 feet high. Based on estimates derived from multiple images of people on the tower's observation platform, I assumed an observer’s eye-height of approximately 45 feet. Since the map units are in meters by default, a quick conversion yields a rounded value of 15 meters. This slight inaccuracy actually errs on the side of the advertiser, slightly boosting the elevation by about 4 feet.

To further give favor to the advertised claims, I’m choosing to ignore a windowed shack located on the tower's westernmost corner that partially obstructs the view. Instead, the entire tower will be treated as a flat surface with equal visibility.

To proceed, we created a new point feature layer and added a point at the center of the lookout tower's location. Before using the Viewshed tool, we added an additional field to the layer's attribute table called OFFSETA, which represents the observer's height mentioned earlier. For all other variables, we used the default values provided by the Viewshed tool and employed a geodesic model to account for the curvature of the Earth.

Output

The output generated by ArcGIS is not immediately intuitive to interpret. The new layer applies color only to the areas that are visible from the lookout tower, blocking them from view. Since the goal is to comprehend the areas that can be seen, this type of coloring presents an inverse representation that lacks utility. To correct this, the symbology of the layer needs to be altered.

Each cell within the viewshed contains either one of two values, indicating whether the cell is visible or not from the observer's standpoint. Using unique colors to classify the layer on these values is the correct approach, however the colors simply need to be changed. By designating the visible cells as "No Color" and the non-visible cells as a dark black color, I can then adjust the layer's transparency to resemble a scene illuminated by a lightbulb, where shadowed regions correspond to areas that cannot be seen, while the brightly lit areas represent those that are visible.

This revised symbology enhances our understanding of the viewshed analysis by providing a visual representation more akin to the way we see light and shadow interact daily.

Results

It is important to acknowledge that the conditions of this model represent the most ideal scenario for visibility. Weather conditions, despite the region's propensity for significant rain and cloud cover, were not taken into account. The presence of tall fir trees, plentiful enough to contribute to the state's nickname, would reduce visibility in some directions, particularly close to the tower, and have also not been factored into the analysis. Finally, while the location provides a broad view of the surrounding area, that visibility is limited due to significant portions of the San Juan Islands being obscured by their own terrain. Nearly the entirety of Orcas Island, for instance, is blocked from view predominantly by Mount Constitution itself.

Despite these limitations, some American and Canadian cities can be indeed be seen, as per the claim. The American town of Bellingham is easily visible and, considering that Mount Baker can be seen 47 miles away, it is plausible that visitors might be able to discern the Vancouver skyline, which is 42 miles distant. Certain parts of nearby Friday Harbor would be visible if the tree line permits, although the mainland town of Anacortes would be concealed by Cypress Island. Likewise, the Canadian city of Victoria remains mostly unseen due to its location in a valley.

With grand panoramic views of the northern Cascade Mountains, and a maximum visibility range of 65 miles before the Salish Sea dips beyond the horizon, it can be concluded that Mount Constitution is indeed an excellent vantage point for observing the Washington State’s northwest corner of islands. Although there were some generous assumptions in the model, the marketing claims do seem to be valid.