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We use radio-wave scattering data to constrain the distribution of ionizedgas in the outer Galaxy. Like previous models, our model for the H II diskincludes parameters for the radial scale length and scale height of the H II,but we allow the H II disk to warp and flare. Our model also includes thePerseus arm. We use a likelihood analysis on 11 extragalactic sources and 7pulsars. Scattering in the Perseus arm is no more than 60% of the levelcontributed by spiral arms in the inner Galaxy, equivalent to a 1 GHzscattering diameter of 1.5 mas. Our analysis favors an unwarped, nonflaringdisk with a 1 kpc scale height, though this may reflect the non-uniform andcoarse coverage provided by the available data. The lack of a warp indicatesthat VLBI observations near 1 GHz with an orbiting station having baselinelengths of a few Earth diameters will not be affected by interstellarscattering at Galactic latitudes |b| ~ 15 degrees. The radial scale length is15--20 kpc, but the data cannot distinguish between a gradual decrease in theelectron density and a truncated distribution. We favor a truncated one,because we associate the scattering with massive star formation, which is alsotruncated near 20 kpc. The distribution of electron density turbulencedecreases more rapidly with Galactocentric distance than does the hydrogendistribution. Alternate ionizing and turbulent agents---the intergalacticionizing flux and satellite galaxies passing through the disk---do notcontribute significantly to scattering. We cannot exclude the possibility thata largely ionized, but quiescent disk extends to >~ 100 kpc, similar to thatfor some Ly-alpha absorbers.Comment: 34 pages, LaTeX2e with AASTeX aaspp4 macro, 9 figures in 9 PostScript  files, accepted for publication in Ap

The Radial Extent and Warp of the Ionized Galactic Disk. II. A Likelihood Analysis of Radio‐Wave Scattering toward the Anticenter