Spectra from the SDSS are obtained by sending light from the target through fiber optic cables to a spectrograph. In the SDSS-III Survey, one thousand objects are analyzed at a time. The 1000 fiber optic cables are held in a precise location by fitting them into a hole drilled in an aluminum plate. The section of the sky captured by one plate is outlined when you select Plates from Advanced Options.
The image on this page is zoomed out by a factor of 256 to reveal the plate boundaries. As you can see, the plates overlap. In combination with the Objects with spectra option selected from Drawing options, an astronomer can see that there are objects in the database that may have more than one spectrum.
