[mapserver-commits] r8687 - trunk/docs/tutorial

[svn at osgeo.org]

Author: pnaciona
Date: 2009-03-09 09:09:00 -0400 (Mon, 09 Mar 2009)
New Revision: 8687

Added:
   trunk/docs/tutorial/example1-3.txt
Log:
add example 1.3 to the tutorial

Added: trunk/docs/tutorial/example1-3.txt
===================================================================
--- trunk/docs/tutorial/example1-3.txt	                        (rev 0)
+++ trunk/docs/tutorial/example1-3.txt	2009-03-09 13:09:00 UTC (rev 8687)
@@ -0,0 +1,51 @@
+.. _example1-3:
+
+===========
+Example 1.3
+===========
+Displaying Classes in a Layer
+-----------------------------
+
+By using non-spatial attribute information in the data, we can create a map
+like this:
+
+.. image: http://biometry.gis.umn.edu/cgi-bin/mapserv.exe?map=/ms4w/apps/tutorial/htdocs/example1-3.map&layer=states_poly&layer=states_line&mode=map
+
+This is what the mapfile looks like: `Example1-3.map<http://biometry.gis.umn.edu/tutorial/example1-3.map>`_.
+
+The mapfile structure, by objects, looks like this:
+
+::
+
+                                  MAP
+      (states_poly) LAYER----------|---------LAYER (states_line)
+                      |                      |
+       (land) CLASS---|---CLASS (water)      |-CLASS
+                  |       |                    |
+            STYLE-|       |-STYLE              |-STYLE</pre>
+
+Our mapfile still only has two layers but the polygon layer has been broken down
+into two classes. Let's have a look at the additional parameters:
+
+**CLASSITEM**
+This keyword is used to specify what attribute to use in separating the class 
+objects. In this example that attribute is "CLASS". If you open the database 
+file associated with this layer's shapefile, you'll see that there's a column 
+(attribute) called "CLASS".
+
+How do we know which attribute to use?  Well, database records in
+            shapefiles are stored in DBF files.  You can open it in a
+            spreadsheet program such as Openoffice.org's Calc, or in a desktop
+            GIS software such as QGIS, Thuban, or ArcView.  If your data came
+            with a metadata (and it should!), you can skim through through that
+            metadata file for attribute information.  You can also use "ogrinfo"
+            to display basic attribute info in your shapefiles--look back at
+            example 1.1 (the last few lines after "Layer SRS WKT:" show the
+            attribute names and types).
+
+**EXPRESSION**
+For each class, we specify what attribute value to use. This is the
+            simplest form of EXPRESSION. EXPRESSIONs can be even more complex
+            than this, allowing one to evaluate regular or logical expressions.
+            Please look at the mapfile reference page to see what you can do
+            with EXPRESSION.