The Zodiac Killer was last seen running into Julius Khan playground by eyewitnesses at Spruce Street. Therefore, a murder committed at Washington and Maple would allow the Zodiac Killer a walking distance of just 86 meters northwards, before heading east along Jackson Street and out of sight from the crime scene. He now has 131 meters to Spruce Street and the seclusion of Presidio Park and Julius Khan playground. This allows him three phases of separation:  Up Maple and east on Jackson  Into the park to reach his vehicle, and  Into his vehicle and over the Golden Gate Bridge. However, something happened as the taxicab approached the intersection of Washington and Maple, that forced a change of plan and Paul Stine to travel one block further west to Washington and Cherry. The reason for this switch could be manyfold, such as pedestrians at the desired location or occupied vehicles in the vicinity of Washington and Maple. Despite all the best laid plans, the Zodiac Killer was still reliant on the timing of the taxicab approaching a populous area with any number of distractions.
In his letter to the San Francisco Chronicle two days after the murder, the Zodiac Killer began his communication "I am the murderer of the taxi driver over by Washington St + Maple St last night, to prove this here is a blood stained piece of his shirt". By his statement of "last night", it is clear he is preparing this letter on Sunday, October 12th 1969. The Zodiac Killer may have scouted the area in advance, highlighting Washington and Maple as his preferred kill site, but this doesn't necessarily mean he knew every street in the area by name. He could have checked a map the following day and noted that his murder occurred at Washington and Cherry, but it didn't appear that this was the case or of high priority to him.
The newspaper headlines the following day were obviously unaware that this was a Zodiac crime, when the San Francisco Chronicle wrote on October 12th "A Yellow Cab driver was found shot to death in his cab last night, the victim of an apparent robbery attempt in Presidio Heights". The article continued, stating "Police said three youngsters saw a scuffle near the cab, which was stopped on Washington Street, near Cherry Street, about 10 pm". Although this should have told the Zodiac Killer the location of the murder site, we are not in a position to determine what time he prepared and sealed this letter with respect to the San Francisco Chronicle publication. If he sealed it before the article's release, he may have been unfamiliar with the road he traveled up after leaving the taxicab. I don't suppose noting down the street name after the murder was high on his priority list. If the letter was prepared after the newspaper publication and he had read it, then writing "I am the murderer of the taxi driver over by Washington St + Maple St last night" could have been a deliberate choice by the Zodiac Killer, signifying that he had knowledge of the destination contained within the trip sheet. There is no reason to conclude his writing of "by Washington St + Maple St" was evidence of his unfamiliarity with the general area he was operating.
October 11th 2019 will mark the 50th anniversary of the murder of Paul Stine with little progress or resolution in sight. One day in the future the mask of the Zodiac Killer will hopefully be removed - the Zodiac circus will stop - and the traveling clowns will not be required to entertain the crowd anymore.