I made some improvements to the offshore county maps, enjoy.
Caveat about maps. Offshore County Maps of California, Oregon and Washington
The geodesic boundaries are calculated using the nearestcounty linelogic. This is not the nearest point of land logic used by the California Bird Records Committee (CBRC), but the closest to a counties outer boundary line. Measuring the distance using the closest point of land logic is problematic. Doing so causes some boundaries to bisect the county's legal boundary. For example, you could be caught speeding within the 3 mile inshore limit in your boat in Orange County by a County Sheriff and you would have to go to court in Orange County, but any birds seen at that same location may be listed in a CBRC report as Los Angeles County.
The nearest county lines are measured using the U.S. Department of Commerce, U.S. Census Bureau, and Geography Division TIGER Shape files.The coastalcounty shape files extend to3 miles offshore (dotted line) as part of their legal county jurisdiction.Many of the 3 mile county distances are measured from small offshorerocky out cropping's and shoals and not just from the mainland or significant offshore islands. These county boundaries are readily visible for some counties e.g. see Del Norte County in California. Note the boundary around Seal Rock and the St. George Reef which causes the county to extend further offshore. The dark solid line is the twelve mile legal state jurisdiction line. By law, counties stop after 3 miles and the state line is an additional twelve miles.
It is my personal belief that birds seen up to 3 miles should count for that county and if beyond 3 miles and within the 3-15 mile state boundary only count for the state. Any bird sightings beyond the 15 mile state line would only count for your ABA list.
The CBRC states on their website that "The Committee reviews records only at the state level. It makes no formal decisions regarding the county in which a particular bird at sea may have occurred, beyond listing the nearest point of land in published reports and in its database." So you are free to use this map as your county list reference. it is totally up to you if you want your county to extend 3, 15 or 200 miles.
For an explanation of how these county boundaries have been established by the California Bird Records Committee (CBRC).
A special thanks to a few folks who provided feedback and direction.
Elias Elias, Paul Lehman, and Alvaro Jaramillo