  We present a method for comparing and combining maps with different
resolutions and beam shapes, and apply it to the Saskatoon, QMAP and COBE/DMR
data sets. Although the Saskatoon and QMAP maps detect signal at the 21 sigma
and 40 sigma levels, respectively, their difference is consistent with pure
noise, placing strong limits on possible systematic errors. In particular, we
obtain quantitative upper limits on relative calibration and pointing errors.
Splitting the combined data by frequency shows similar consistency between the
Ka- and Q-bands, placing limits on foreground contamination. The visual
agreement between the maps is equally striking. Our combined QMAP+Saskatoon
map, nicknamed QMASK, is publicly available at
www.hep.upenn.edu/~xuyz/qmask.html together with its 6495x6495 noise covariance
matrix. This thoroughly tested data set covers a large enough area (648 square
degrees -- currently the largest degree-scale map available) to allow a
statistical comparison with COBE/DMR, showing good agreement.
