Each time the map updates (every few minutes) the contours change, and there are little "redline islands" that jump around. Below I captured a screen shot that includes the legend plus a bit of a "redline island".
The legend says:
GPS Service Contour
RAIM Service Outage: RNP 1 (Red Line): RNP 3 (Green LIne): EnRoute (Yellow Line)
Color Scale is Position Dilution of Precision (PDOP)
Question: What is a RAIM service outage, what is RNP, what does EnRoute mean, and why do these redlines jump around so quickly? Are these generally closed contours, such that whatever they indicate is true for the entire area inside the contour, or is it true only along the line itself?