In general there can be more that one data source available from each station.   
For instance the one station may be capable of providing high and low resolution   
data as well as state-of-health data, and a log of its availability.
   
The IRIS DMC uses a location code to identify different dsata sources from   
the same thation. Common location codes are:   
   
--   
00   
10   
   
but there may be others. IRIS will accept wildcards.