title: Geometry column: STGeomFromText and SRID (what is an SRID?)
body: <p>I'm playing with the new geography column in SQL Server 2008 and the STGeomFromText function.  Here is my code (works with AdventureWorks2008)</p>
  
  <pre><code>DECLARE @region geography;
  set @region = geography::STGeomFromText('POLYGON((
          -80.0 50.0, -90.0 50.0,
          -90.0 25.0, -80.0 25.0,
          -80.0 50.0))', 4326);
  
  SELECT @region;
  </code></pre>
  
  <p>My question is about the 4326 in the code.  It is supposed to be a spacial Reference ID.  When I go to MSDN there isn't a lot on it.  If I change the value to 56 I get an error telling me the value must be in the sys.spatial_reference_systems table.</p>
  
  <p>You can look at that table by executing:</p>
  
  <pre><code>select * from sys.spatial_reference_systems 
  </code></pre>
  
  <p>There is a well_known_text column in that table, but it doesn't tell me much.  The value for 4326 is:</p>
  
  <pre><code>GEOGCS["WGS 84", DATUM["World Geodetic System 1984", ELLIPSOID["WGS 84", 6378137, 298.257223563]], PRIMEM["Greenwich", 0], UNIT["Degree", 0.0174532925199433]]
  </code></pre>
  
  <p>Can anyone explain this mystery to me?  What is the SRID?</p>