  Three dimensional galaxy clustering measurements provide a wealth of
cosmological information. However, obtaining spectra of galaxies is expensive,
and surveys often only measure redshifts for a subsample of a target galaxy
population. Provided that the spectroscopic data is representative, we argue
that angular pair upweighting should be used in these situations to improve the
3D clustering measurements. We present a toy model showing mathematically how
such a weighting can improve measurements, and provide a practical example of
its application using mocks created for the Baryon Oscillation Spectroscopic
Survey (BOSS). Our analysis of mocks suggests that, if an angular clustering
measurement is available over twice the area covered spectroscopically,
weighting gives a $\sim$10-20% reduction of the variance of the monopole
correlation function on the BAO scale.
