  Strong nebular emission lines are an important diagnostic tool for tracing
the evolution of star-forming galaxies across cosmic time. However, different
observational setups can affect these lines, and the derivation of the physical
nebular properties. We analyze 12 local star-forming galaxies from the COS
Legacy Spectroscopy SurveY (CLASSY) to assess the impact of using different
aperture combinations on the determination of the physical conditions and
gas-phase metallicity. We compare optical spectra observed with the SDSS
aperture, which has a 3" of diameter similar to COS, to IFU and longslit
spectra, including new LBT/MODS observations of five CLASSY galaxies. We
calculate the reddening, electron densities and temperatures, metallicities,
star formation rates, and equivalent widths (EWs). We find that measurements of
the electron densities and temperatures, and metallicity remained roughly
constant with aperture size, indicating that the gas conditions are relatively
uniform for this sample. However, using the IFU observations of 3 galaxies, we
find that the E(B-V) values derived from the Balmer ratios decrease ( by up to
53%) with increasing aperture size. The values change most significantly in the
center of the galaxies, and level out near the COS aperture diameter of 2.5".
We examine the relative contributions from the gas and stars using the
H$\alpha$ and [OIII] $\lambda$5007 EWs as a function of aperture light
fraction, but find little to no variations within a given galaxy. These results
imply that the optical spectra provide nebular properties appropriate for the
FUV CLASSY spectra, even when narrow 1.0" long-slit observations are used.
