[pct-l] Erik the Black's Maps: They're Excellent!!!

[Kathy Walter]

I'm doing some planning for the JMT today and I'm looking at Erik the  
Black's Atlas, Wilderness Press's Data Book and Tom Harrison's maps  
and all three have different elevations for identical points, some by  
just a few feet, some by a couple hundred. Which source is considered  
most accurate? And out of curiosity, does anyone know how these folks  
arrived at their numbers? Are they all just out there with their own  
altimeters getting their own reads? I assumed there was an official  
source for this kind of information.