  We present a broadband map of polarized diffuse emission at 167-198 MHz
developed from data from the Murchison Widefield Array (MWA). The map is
designed to improve visibility simulation and precision calibration for 21 cm
Epoch of Reionization (EoR) experiments. It covers a large swath - 11,000 sq.
deg. - of the Southern Hemisphere sky in all four Stokes parameters and
captures emission on angular scales of 1 to 9 degrees. The band-averaged
diffuse structure is predominantly unpolarized but has significant linearly
polarized structure near RA = 0 h. We evaluate the accuracy of the map by
combining it with the GLEAM catalog and simulating an observation from the MWA,
demonstrating that the accuracy of the short baselines (6.1-50 wavelengths) now
approaches the accuracy of the longer baselines typically used for EoR
calibration. We discuss how to use the map for visibility simulation for a
variety of interferometric arrays. The map has potential to improve calibration
accuracy for experiments such as the Hydrogen Epoch of Reionization Array
(HERA) and the forthcoming Square Kilometre Array (SKA) as well as the MWA.
