Like New Jersey, Washington uses a bipartisan commission to draw its lines.  Unlike New Jersey, the rules for Washington provide that, to the extent possible, the lines should respect geographical boundaries and the boundaries of political subdivisions.  Additionally, the lines are required to be fair and promote competitive districts.

And in a pattern that we have seen in other states, the districts in the major metropolitan areas now have excess voters and the more rural districts are now short voters.  And in Washington, that could hurt the Republicans.  The three districts currently held by Republicans (Third District in southwest Washington, Fourth District in central Washington, and Fifth District in eastern Washington) are a combined 50,000 people short.  The Sixth District in northwestern Washington is another 32,000 people short.  Meanwhile, the most Democratic district in the state (Seventh District — Seattle) has around 40,000 excess population and the First District (north central Washington) and Eighth District (eastern King County and central Washington) have a combined 25,000 excess population.  The only district that is close to being a majority minority district is the Ninth District (part of Seattle and its eastern suburbs).

There are some maneuvers that could reduce the number of split counties.  For example, King County is large enough to contain two whole districts with some left over.  Thus, I moved the part of the Seventh District in Snomish County to the Second District.  And I exchanged some precincts in Snomish County from the First District to the Second District while giving the part of the Second District in Whatcom County to the First District.  Likewise, I gave all of the Tenth District precincts in Mason County to the Sixth (which also has to expand into Thurston County and additional Thurston County precincts to the Third District.  To bring the Fifth up to quota, I gave all of the precincts in Walla Walla County to the Fifth District along with the Eastern half of Okanogan County.  That, in turn, required the Fourth District to expand westward in Whatcom County.  An argument can be made for rearranging the Fourth and Fifth Districts to give the southeastern part of the state to the Fourth District and leaving the Fifth District to the northeastern part of the state.

Before looking at whether a more compact map can be made with east-west lines for the Fourth and Fifth District rather than the current north-south lines, the overall map is likely to maintain the status quo.  The Third District, which is already a reddish swing district would get just a bit closer.  The Fifth District would stay a lean to safe Republican District and the Fourth District would stay solid Republican.  On the Democratic side, the Eighth District would become slightly more Democratic moving it into the lean Democratic sphere with the other districts being safe or solid Democrat districts.

Right now the big obstacle to more county based lines are the residences of the current representatives.  You have four representatives living in King County — the First, Seventh, Eighth, and Ninth.  If there were only three representatives living in King County, you could avoid drawing a district that runs from King County to the Canadian border and eliminate the unnecessary split in Skagit County and draw better splits in Snomish, King, and Pierce Counties.  As noted above, King should have two whole districts and one partial rather than one whole and three partials, and Pierce and Snomish should have one whole and one partial rather than the current three partials in Pierce and two partials in Snomish.    Additionally, the two representatives living in the northwestern part of Pierce (Sixth and Tenth) also hinder the division of Pierce into one whole and one partial.

But, at the end of the day, while you may have some minor rearrangements (or major if you want to make the Fourth a little less unwieldy), the bottom line is that the split in Washington is likely to stay 7-3.