NCGS Observation Bases
How an observation of a site was made: standing on it, from the desk, or by asking someone who was. A later field observation overrides a desk one, since the latest observation wins (#130).
At the desk
Judged from maps, aerial or satellite imagery, or records, without visiting.
On site
The observer stood at the site.
Remotely, by asking
Reported by someone at the site, by phone or message, and recorded by the observer.