  The stochastic gravitational-wave background (SGWB) created by astrophysical
sources in the nearby Universe is likely to be anisotropic. Upper limits on
SGWB anisotropy have been produced for all major data-taking runs by the
ground-based laser interferometric detectors. However, due to the challenges
involved in numerically inverting the pixel-to-pixel noise covariance matrix,
which is necessary for setting upper limits, the searches accounted for angular
correlations in the map by using the spherical harmonic basis, where
regularization was relatively easier. This approach is better suited though for
extended sources. Moreover, the upper-limit maps produced in the two different
bases are seemingly different. While the upper limits may be consistent within
statistical errors, it was important to check whether the results would remain
consistent if the full noise covariance matrix was used in the pixel basis.
Here, we use the full pixel- to-pixel Fisher information matrix to create
upper-limit maps of SGWB anisotropy. We first perform an unmodeled search for
persistent, directional gravitational-wave sources using folded data from the
first (O1) and second (O2) observing runs of Advanced LIGO and show that the
results are consistent with the upper limits published by the LIGO-Virgo
Collaboration (LVC). We then explore various ways to account for the
pixel-to-pixel Fisher information matrix using singular-value decomposition and
Bayesian regularization schemes. We do not find evidence for any SGWB signal in
the data and the upper limits are consistent with the LVC results within
statistical errors. Through an injection study, we show that they are all valid
95\% upper limits, that is, the upper limit in a pixel is less than the
injected signal strength in less than 5\% of the pixels.
