Can I restrict a SQL Server spatial field to hold values of specified spatial types and SRIDs? I am trying to understand geography data types so I can integrate my database more closely with GIS processes. From my reading, it appears that a geography field can hold many different types of objects. 

If this is the case, how do I prevent someone from loading, say, polygons into a field that I want to use to retain points, or loading points in the incorrect coordinate system? Will I have to check the data type and projection each time I write a query so I don't get erroneous results?
The usual way to do this would be through a check constraint.  

The properties you want to check are .STSrid and .STGeometryType()

So something like

ALTER TABLE Test   
    ADD CONSTRAINT chk_shape_gtype_srid   
    CHECK (
        shape.STSrid = 4326 AND 
        shape.STGeometryType() in ('POLYGON','MULTIPOLYGON')
    );