  We study the photometric properties of stars in the data archive of the Sloan
Digital Sky Survey (SDSS), the prime aim being to understand the photometric
calibration over the entire data set. It is confirmed that the photometric
calibration for point sources has been made overall tightly against the SDSS
standard stars. We have also confirmed that photometric synthesis of the SDSS
spectrophotometric data gives broad band fluxes that agree with broad band
photometry with errors no more than 0.04 mag and little tilt along the wide
range of colours, verifying that the response functions of the SDSS 2.5 m
telescope system are well characterised. We locate stars in the SDSS
photometric system, so that stars can roughly be classified into spectral
classes from the colour information. We show how metallicity and surface
gravity affect colours, and that stars contained in the SDSS general catalogue,
plotted in colour space, show the distribution that matches well with what is
anticipated from the variations of metallicity and surface gravity. The
colour-colour plots are perfectly consistent among the three samples, stars in
the SDSS general catalogue, SDSS standard stars and spectrophotometric stars of
Gunn & Stryker, especially when some considerations are taken into account of
the differences (primarily metallicity) of the samples. We show that the g-r -
inverse temperature relation is tight and can be used as a good estimator of
the effective temperature of stars over a fairly wide range of effective
temperatures. We also confirm that the colours of G2V stars in the SDSS
photometric system match well with the Sun.
