  The stages before the formation of stars in molecular clouds are poorly
understood. Insights can be gained by studying the properties of quiescent
clouds, such as their magnetic field structure. The plane-of-the-sky
orientation of the field can be traced by polarized starlight. We present the
first extended, wide-field ($\sim$10 $\rm deg^2$) map of the Polaris Flare
cloud in dust-absorption induced optical polarization of background stars,
using the RoboPol polarimeter at the Skinakas Observatory. This is the first
application of the wide-field imaging capabilities of RoboPol. The data were
taken in the R-band and analysed with the automated reduction pipeline of the
instrument. We present in detail optimizations in the reduction pipeline
specific to wide-field observations. Our analysis resulted in reliable
measurements of 641 stars with median fractional linear polarization 1.3%. The
projected magnetic field shows a large scale ordered pattern. At high
longitudes it appears to align with faint striations seen in the Herschel-SPIRE
map of dust emission (250 $\mu m$), while in the central 4-5 deg$^2$ it shows
an eddy-like feature. The overall polarization pattern we obtain is in good
agreement with large scale measurements by Planck of the dust emission
polarization in the same area of the sky.
