No - every pixel in the image is recomputed every time. The resulting texture is applied to both the flat map and the sphere. 'Computing' a pixel means converting it from pixel to lat-lon to spherical coordinates, checking for satellite visibility, and coloring the pixel accordingly. This conversion is necessary for me to get a value for each pixel.Do you have a basic texture on which you only highlight certain areas?
OP would not have to do this conversion. He already has values at various lat lons. What he could do is plot his points in a rectangular viewport (with lat-lon dimensions) and triangulate those points to get polygons. GL will automatically do the color interpolation for him, assuming he applies colors to each point. He would then need to overlay his map of the continents. The hardest part here is the triangulation. If there aren't many points and they don't change location with time, he could do it by hand. Otherwise he's going to have to apply an algorithm such as Delaunay Triangulation.