But, this discussion of the geography of Cascadia, what is inside the region and what is not, is pretty vital to every other discussion about Cascadia. Where you draw the borders defines what politics, culture and social structures belong inside Cascadia.
There are three major lines of thinking in terms of defining what is Cascadia.
1. Oregon and Washington, maybe some of B.C.
This is the simplest map and the worst of all three. Basically take the state and provincial boundaries for the three existing subdivisions and there you go.
I'm not even going to bother trying to show you this map. What, don't you know where Washington and Oregon are?
It lacks the elegance or real world common sense of both of the maps below. It ignores any similarity the Alaska or California might allow parts of them to be included. Bad map.
This is definition of the region bases its definition on natural features. This is a strictly accurate definition based on the original concept of Cascadia from the 1970s. The original Cascadian thinkers brought a lot of ecology into their definition, so a bioregion made absolute sense to them.
Especially when you look a map of the "Salmon Nation," it looks surprisingly similar to the Cascadian bioregion.
3. West of the mountains.
The limitations of the bioregion map is that it includes so many human communities that are different from the population core of Cascadia. In short, there is very little cultural, social or political connections between Moses Lake and Seattle.
The best map of this region is from Colin Woodard's "American Nations," basically showing a Chile shaped country hugging the Pacific Coast.
Even when places like the interior of Washington and Oregon were attached to the Willamette Valley and Puget Sound, it didn't take long for them to want to leave. In a much larger, bioregional nation, the interior communities would constantly be at odds with the urban coastal cities. While geographically close to Seattle, Portland and Vancouver, they are culturally and politically closer to the broader interior west.
May favorite map, if you were wondering, is #3. And, I know I'm well in the minority here. Most people it seems want to include some portion east of the Cascades. While I think there is some parts of Cascadia that are leaking across the mountains (Cle Elum and Hood River), more often than not, those dry side places have more to do with Wyoming or Idaho than Edmonds.
In a recent discussion on the Cacadia subreddit, the bioregional map by default chosen as the better map (and with percentages). Though, the coastal areas scored the highest overall, much of the interior was still included in the final map. Strangely (to me at least) the Bay Area scored very low.