Essential Criteria for Yield Curve Construction

Following a recent analysis of interest rates and their movements, a financial analyst is attempting to construct the yield curve for a specific bond issuer. To properly project future interest rates along different maturities, the analyst understands that he needs to utilize various yield points from instruments across the maturity spectrum.

Which of the following criteria is most essential in the construction of the yield curve, particularly when considering the proper selection of rates for bonds of similar risk characteristics and liquidity?