2.5. Static map with two layers#

2.5.1. View examples#


In this example, the image is generated to the source of the URL:


Most traditional MapServer examples are shown in this way.

This example is slightly different from the previous one, where the color of the polygon has been modified.

2.5.2. Mapfile description#

First take a look at the MapFile that this example uses mfa2.map ), This Mapfile defines two layers:

 3    EXTENT -180 -90 180 90
 4    SIZE 600 300
 5    SHAPEPATH "/gdata"
 6    IMAGECOLOR 255 255 255
 7    LAYER
 8        NAME "world-country"
 9        DATA "wcountry.shp"
10        STATUS OFF
11        TYPE POLYGON
12        CLASS
13            NAME "States"
14            STYLE
15                COLOR 232 232 232
16            END
17        END
18    END
19    LAYER
20        NAME "country-line"
21        DATA "wcountry.shp"
22        STATUS OFF
23        TYPE LINE
24        CLASS
25            NAME "State Boundary"
26            STYLE
27                COLOR 132 132 32
28            END
29        END
30    END

It’s important to remember that MapServer’s render layers are in the order they are specified in the mapfile. The last layer in the Mapfile is the top layer of the map rendering result, building the map on top of all the previous layers. This means that details shown earlier in the Mapfile (ie, lower layers in the map image) may be obscured. This is most important when rendering polygon layers, since polygons can be filled with a specified color. If the map server renders a point layer (that is, for example, the location of a city), then the render state represents a polygon layer, and the city will not be visible unless the specified polygon layer color is transparent.

This problem is easily remedied by defining the polygon layer in front. Polygons can also be rendered as a series of lines (ie, a line layer). Since a line is one-dimensional, there is no area to fill, so the details of the layers below are still visible. When there is no fill color, the specified color is: -1,-1,-1, which can also achieve the effect of transparency.

The structure of MapFile looks like this:


Compared to the previous Mapfile, the changes are as follows:

Open the file:diff_mfa2_mfa1.html

Here, the original layer is divided into two layers. The first layer is still a polygon layer, but there is no OUTLINECOLOR attribute in the style anymore. The TYPE of the second layer is LINE and the color value is different from the OUTLINECOLOR in the first example. This produces a slightly different image from the first example.

2.5.3. Further explanation#

Here is an explanation of why this is done. If we continue to add layers on top of the state layer, the contours are most likely to be masked by these layers. To be able to see the borders and add other layers, we have to separate the borders layer from the state polygon layer and place it on top of the other other layers. There is an order in how to define/add layers, which will be explained later. Here you just need to remember according to “Later on top” (layers defined later will be displayed on the top).