There are many metaphors for the space you are about to enter. "Brass Tacks", "Under the Hood" and "Rubber Meets the Road" would be appropriate. The bottom line is that, all high level considerations (such as vision and GMA and carrying capacity, etc.) notwithstanding, the Comp Plan ground zero is the land. The land is divided into various broad land use categories (Activity Centers, Rural Lands, Resource Lands are the official ones) and an unofficial but real 4th category of Public Spaces like National, State and Local parks along with conservation easements that in many cases allow public access; these easements are held principally by the San Juan Preservation Trust and the Land Bank.
Regardless of the land use category, the basic land unit is a parcel, which could be from a fraction of an acre to thousands of acres. Each parcel has an identifying number ("tax parcel number" or TPN) along with a host of characteristics: who owns it, what it's land use designation is, what it's density assignment is, how big it is, whether it is located on waterfront, etc.
San Juan County has a lot of parcel information available on line. There is the GIS information center, which has endless maps of various activities, and the GIS Open Data resource (click the explore link), containing semi trucks full of data that can either be displayed geographically or analyzed statistically. In addition, there are the Assessors Parcel Data Search and the Polaris Property Search services.
Information, tho, does not mean knowledge, and knowledge does not mean wisdom. Virtually no one has drilled into the information to condense it, ask relevant questions, and generate information. Even more wincing, no one has taken the information and made a thorough attempt to divine how that knowledge can be translated and used to achieve wisdom.
Keep San Juans Wild has created a database that combines several databases available at the Open Data resources cited above. This database contains information on all ~17,000 individually owned tax parcels comprising the ~112,000 acres in the county as of January 2017. Because of the generosity of residents and governmental entities since the county began, a considerable amount of county land has been preserved in the form of parks and easements: over 25,000 acres or a bit under 25%. This number is derived from analyzing all parcels in the county that have a tax exempt status. A sample of tax exempt parcels for Orcas Island sorted and summarized by owner is available here. (Note: PIN is the Tax Parcel Number or TPN.) The biggest exempt parcels are parks. On Orcas, for example, well over half of the ~10,000 acres of tax exempt parcels are owned by the State of Washington; the biggest single parcel is Moran State Park (at ~4900 acres).
For those motivated to drill into the data, a summary of the data sources and fields for the database cited above is located here.
There are many unasked, unanswered, uncertain and unresolved (yet critical) questions related to what all this information means in terms of the essential big-picture issues before the county. Those big-picture issues include consistency with the Growth Management Act (and the county's vulnerability to a lawsuit), consistency with carrying capacity (for example, does the county have enough water?), consistency with the vision statement (at what point does the county lose the quiet rural slow qualities that brought and keep residents here or, as tourists, coming, and morphs into a Nantucket West?)
Absent serious public engagement (see the Take Action section), these questions will neither be addressed nor answered. The plan as it exists is essentially toothless; what happens without intervention will be market driven, as it has been here for decades, and as it has been in those east coast resort communities many do not wish were a default business as usual model for San Juan County.