Comparing Checkboard's example to the real airport aerial pix - at those locations (NOT TO SCALE) there are
small green boxes astride taxi lines, containing numbers corresponding to the GEOGRAPHIC POSITION MARKINGS on the chart.
E.G. (at GPM 50) -
https://www.google.com/maps/place/Se...4d-122.3088165
The sample chart IS labeled as "
Low Visibility Taxi Routes" - so I think those are just additional markings to tell pilots who cannot see anything else at the moment (in fog, etc.) exactly where they are on the ramp/apron.