MapServer6.4.1教程学习--显示图层内类别(1-3)

示例1.3

显示层内类别

（http://www.mapserver.org/tutorial/example1-3.html#example1-3）

利用数据内非空间属性信息，我们可以生成一幅如下所示地图：

MapFile结构

下面是示例1.3的mapfile文件：

#The annotated map file (sort of)

#Created by Pericles S. Nacionales for the MapServer tutorial

#20050408

#

#MapServer map file uses the pound sign (#) to denote the start of a line

#comment--each line that needs to be commented has to be prepended with a"#".

#

#Map files begin with MAP keyword to signify the start of the map object.

#Well, the entire map file is THE map object. Enclosed between MAP and END

#at the very bottom of this map file, are keyword/value pairs and other

#objects.

MAP

  IMAGETYPE     PNG

  EXTENT        -97.238976 41.619778 -82.122902 49.385620

  SIZE          400 300

  SHAPEPATH     "../data"

  IMAGECOLOR    255 255 255

 

  # Layer objects are defined beneath the mapobject.  You need at least one

  # layer defined in your map file before youcan display a map...  You can

  # define as many layers as you'd likealthough a limit is typically hard-coded

  # in map.h in the MapServer source.  The default limit is set at 100.  You'd

  # have to have a very specialized applicationto need more than 100 layers in

  # your application.

 

  # Start of LAYER DEFINITIONS---------------------------------------------

  LAYER # States polygon layer begins here

    NAME        states_poly

    DATA        states_ugl

    STATUS      OFF

    TYPE        POLYGON

 

    # CLASSITEM defines the non-spatialattribute that you will be using to

    # separate a layer into classes.  This attribute will be in the DBF file

    # of your shapefile (it will be differentfor each data format).  In this

    # example the shapefile states_ugl has anassociated database

    # (states_ugl.dbf) that contains anattribute called "CLASS".  Youwill be

    # using two values in the CLASS attributeto separate the classes (also

    # called themes) used in this layer--landand water.  CLASSITEM is used in

    # association with the EXPRESSION parameterin the CLASS object.  See below.

    CLASSITEM   "CLASS"

 

    # The class object is defined within thelayer object.  You can define as

    # many classes as you need (well, there arelimits as with layers, but it's

    # senseless to define more than ten on a"normal" layer.  There are

    # situations, however, where you might haveto do it.)

    CLASS

      NAME 'States'

      EXPRESSION 'land' # Only polygons where"CLASS" = 'land' will be drawn.

 

      # There are styles in a class, just likethere are classes in a layer,

      # just like there are layers in amap.  You can define multiple styles in

      # a class just as you can define multipleclasses in a layer and multiple

      # layers in a map.

      STYLE

        COLOR      232 232 232

      END

    END

    CLASS

      NAME 'Water'

      EXPRESSION 'water' # Only polygons where"CLASS" = 'water' will be drawn.

      STYLE

        COLOR      198 198 255

      END

    END

  END # States polygon layer ends here

 

  LAYER # States line layer begins here

    NAME        states_line

    DATA        states_ugl

    STATUS      OFF

    TYPE        LINE

 

    CLASSITEM   "CLASS"

    CLASS

      NAME      'State Boundary'

      EXPRESSION 'land'

      STYLE

        COLOR   32 32 32

      END

    END

  END # States line layer ends here

  # End of LAYER DEFINITIONS-------------------------------

 

END# All map files must come to an end just as all other things must come to.

 

Mapfile的对象结构如下所示：

MAP

(states_poly)LAYER----------|---------LAYER (states_line)

|                        |

(land)CLASS---|---CLASS (water)        |-CLASS

|         |                      |

STYLE-|         |-STYLE                |-STYLE

 

关键字：

Mapfile仍只有两个层，但是多边形层被拆分为两个不同类型。让我们看一看增加的参数：

CLASSITEM

     这个关键字用来指定拆分类对象时用到的属性。此例中这个属性是”CLASS”.如果你打开这层shapefile文件关联的数据库文件，你就看发现这里面有一例（属性）是“CLASS”。

我们是如何知道要用哪个属性呢？shapefile文件的数据库记录是存在DBF文件里面的。你可以用Openoffice组织的Calc之类的电子表格软件，和QGIS，Thuban或ArcView之类的桌面GIS软件打开它。如果你的数据带有元数据(本应如此),你可以通过元数据文件来浏览属性信息。复习下示例1.1（Layer SRS WKT之后的最后几行显示了属性名称和类型），你也可以用ogrinfo工具来显示shapefile文件中的基本属性信息。

EXPRESSION

     指定使用类中的哪个属性值。这是EXPRESSION最简单的形式。EXPRESSION在使用正则表达式或逻辑表达式后会比这个更加复杂。请查看mapfile参考手册中的Expressions看看你能够用EXPRESSION做些什么。

 

 

 

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