Since I cant stand it when Seattle is left out of the topics here I thought I would present to you the official SEA spotters locations.
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On 154th and 188th you can likely count on a visit from the POSeattle police if a Joe Nosey decides you look suspicious.
At the SPU site you are less likey to be bothered and you will get some great straight on shots of the aircraft.
Air Cargo Rd is kinda off limits and viewing is real limited and blocked by Cargo hangers....I have heard the UAL cargo is opened for shooting but I was refused a chance to shoot there when I asked and presented some of my work to the facility supervisor a couple of month back...they used the security excuse.
Raddison Hotel parking...You'll have to pay for parking and the views are somewhat obstructed by freeways fences light poles and buses passing by frequently.
Thus far the only place I haven't felt the feeling of being watched and was able to relax and enjoy spotting is at Tyee Golf Club, the management is happy to let you shoot aircraft till your heart content as long as you first ask. They will let you go down on the greens if you have a metal helmet...the closer you can get to 34L the better quality shots You'll get.
If anyone knows of better locations post them to this thread.