  We have mapped HCN and HCO$^{+}$ (J = 1 $\to$ 0) line emission toward a
sample of seven star-forming regions (with 12 + log[O/H] range from 8.34 to
8.69) in the outer Milky Way (Galactocentric distance > 9.5 kpc), using the
14-meter radio telescope of the Taeduk Radio Astronomy Observatory (TRAO). We
compare these two molecular lines with other conventional tracers of dense gas,
millimeter-wave continuum emission from dust and extinction thresholds ($A_{V}
\geq 8$ mag), inferred from the $^{13}$CO line data. HCN and HCO$^{+}$
correlate better with the millimeter emission than with the extinction
criterion. A significant amount of luminosity comes from regions below the
extinction criterion and outside the millimeter clump for all the clouds. The
average fraction of HCN luminosity from within the regions with $A_{V} \geq 8$
mag is $0.343\pm0.225$; for the regions of millimeter emission, it is
$0.478\pm0.149$. Based on a comparison with column density maps from Herschel,
HCN and HCO$^{+}$ trace dense gas in high column density regions better than
does $^{13}$CO. HCO$^{+}$ is less concentrated than HCN for outer Galaxy
targets, in contrast with the inner Galaxy sample, suggesting that metallicity
may affect the interpretation of tracers of dense gas. The conversion factor
between the dense gas mass ($M_{dense}$) and line luminosities of HCN and
HCO$^{+}$, when integrated over the whole cloud, is comparable with factors
used in extragalactic studies.
