Basic geometry itself can magnify these other
errors with a principle called "Geometric Dilution of Precision" or GDOP.
It sounds complicated but the principle is quite simple.
There are usually more satellites available than a receiver needs to fix a position, so
the receiver picks a few and ignores the rest.
If it picks satellites that are close together in the sky the intersecting circles that
define a position will cross at very shallow angles. That increases the gray area or error
margin around a position.
If it picks satellites that are widely separated the circles intersect at almost right
angles and that minimizes the error region.
Good receivers determine which satellites will give the lowest GDOP.