The Pacific Steam Navigation Company was one of the great early steamship lines, established in 1838 by William Wheelwright, a native of Newburyport, Massachusetts and a graduate of Philips Andover. Wheelwright began with a contract from the Chilean government for coastal freight and passenger service. The lack of wind on this coast motivated him to invest in steamships. The company won British mail contracts and by1873 it had the largest merchant steamer fleet in the world.
The ship depicted is the 512-foot long SS Orcoma, launched in 1908, Pacific Lines’ first ship over 10,000 tons. Before the Panama Canal opened in 1914, steamship companies offered service across the Isthmus on the Panama Railroad to a steamer waiting at the other end. Pacific Lines however refused to do so because of a rate dispute with the Railroad. It’s likely therefore that the link shown in the poster’s route map indicates service through the Canal; thus the poster is dated after the Canal was complete.