  We analyse the evolution of coronal plasma upflows from the edges of AR
10978, which has the best limb-to-limb data coverage with Hinode's EUV Imaging
Spectrometer (EIS). We find that the observed evolution is largely due to the
solar rotation progressively changing the viewpoint of nearly stationary flows.
From the systematic changes in the upflow regions as a function of distance
from disc centre, we deduce their 3D geometrical properties as inclination and
angular spread in three coronal lines (SiVII, FeXII, FeXV). In agreement with
magnetic extrapolations, we find that the flows are thin, fan-like structures
rooted in quasi separatrix layers (QSLs). The fans are tilted away from the AR
centre. The highest plasma velocities in these three spectral lines have
similar magnitudes and their heights increase with temperature. The spatial
location and extent of the upflow regions in the SiVII, FeXII and FeXV lines
are different owing to (i) temperature stratification and (ii) line of sight
integration of the spectral profiles with significantly different backgrounds.
We conclude that we sample the same flows at different temperatures. Further,
we find that the evolution of line widths during the disc passage is compatible
with a broad range of velocities in the flows. Everything considered, our
results are compatible with the AR upflows originating from reconnections along
QSLs between over-pressure AR loops and neighboring under-pressure loops. The
flows are driven along magnetic field lines by a pressure gradient in a
stratified atmosphere. We propose that, at any given time, we observe the
superposition of flows created by successive reconnections, leading to a broad
velocity distribution.
