...
The Quay should be placed to correspond as precisely as possible with the estimated boarding position of a vehicle, usually on the front door of the vehicle or the exit point of a sea vessel. For a bus, this point is primarily the edge of the pavement or platform at the tactile paving mark. When no tactile paving exists the position is estimated. When the stop has no pavement the general position is estimated based on how the bus may fit into the existing space, placement of signs or shelters, or the otherwise most logical location to stop a bus along the road.
...
A precise placement reduces the need for future revisions of data and makes pedestrian routing more predictable.
...