more fleshing out of spatial ref section

git-svn-id: http://svn.osgeo.org/postgis/trunk@2975 b70326c6-7e19-0410-871a-916f4a2858ee

diff --git a/doc/using_postgis.xml b/doc/using_postgis.xml
index 087b65d5a20e9424efe5a9ed26f573e38c108055..ee39c5d19ce07c7794681c9620c97273fb93decc 100644 (file)
--- a/doc/using_postgis.xml
+++ b/doc/using_postgis.xml
@@ -276,8 +276,16 @@ geometry
          <para>Some of the more commonly used spatial reference systems are: <ulink url="http://spatialreference.org/ref/epsg/4326/">4326 - WGS 84 Long Lat</ulink>, 
                        <ulink url="http://spatialreference.org/ref/epsg/4269/">4269 - NAD 83 Long Lat</ulink>, 
                        <ulink url="http://spatialreference.org/ref/epsg/3395/">WGS 84 World Mercator</ulink>,
-                       <ulink url="http://spatialreference.org/ref/epsg/2163/">US National Atlas Equal Area</ulink>
-         </para>
+                       <ulink url="http://spatialreference.org/ref/epsg/2163/">US National Atlas Equal Area</ulink>,
+                       Spatial reference systems for each NAD 83, WGS 84 UTM zone - UTM zones are one of the most ideal for measurement, but only cover 6-degree regions.
+       </para>
+       <para>
+               Various US state plane spatial reference systems (meter or feet based) - usually one or 2 exists per US state.  Most of the meter ones are in the core set, but many of the 
+               feet based ones or ESRI created ones you will need to pull from <ulink url="http://spatialreference.org">spatialreference.org</ulink>.
+       </para>
+       <para>
+               For details on determining which UTM zone to use for your area of interest, check out the <ulink url="support/wiki/index.php?plpgsqlfunctions">utmzone PostGIS plpgsql helper function</ulink>.
+       </para>
                        
       <para>The <varname>SPATIAL_REF_SYS</varname> table definition is as
       follows:</para>