  With modern large scale spectroscopic surveys, such as the SDSS and LSS-GAC,
Galactic astronomy has entered the era of millions of stellar spectra. Taking
advantage of the huge spectroscopic database, we propose to use a "standard
pair" technique to a) Estimate multi-band extinction towards sightlines of
millions of stars; b) Detect and measure the diffuse interstellar bands in
hundreds of thousands SDSS and LAMOST low-resolution spectra; c) Search for
extremely faint emission line nebulae in the Galaxy; and d) Perform photometric
calibration for wide field imaging surveys. In this contribution, we present
some results of applying this technique to the SDSS data, and report
preliminary results from the LAMOST data.
