  We show that a large-area imaging survey using narrow-band filters could
detect quasars in sufficiently high number densities, and with more than
sufficient accuracy in their photometric redshifts, to turn them into suitable
tracers of large-scale structure. If a narrow-band optical survey can detect
objects as faint as i=23, it could reach volumetric number densities as high as
10^{-4} h^3 Mpc^{-3} (comoving) at z~1.5 . Such a catalog would lead to
precision measurements of the power spectrum up to z~3-4. We also show that it
is possible to employ quasars to measure baryon acoustic oscillations at high
redshifts, where the uncertainties from redshift distortions and nonlinearities
are much smaller than at z<1. As a concrete example we study the future impact
of J-PAS, which is a narrow-band imaging survey in the optical over 1/5 of the
unobscured sky with 42 filters of ~100 A full-width at half-maximum. We show
that J-PAS will be able to take advantage of the broad emission lines of
quasars to deliver excellent photometric redshifts, \sigma_{z}~0.002(1+z), for
millions of objects.
