Table of Contents for

Web Mapping Illustrated

Chapter 4 described how to access and install the MS4W package. You might want to look at the MS4W portion of that chapter and review how to start the web server. A custom application will be built later in this chapter, but first you need to understand how MapServer works in the MS4W environment.

MS4W comes with a version of the Apache HTTP web server. The MapServer program is stored in Apache’s cgi-bin folder, the main location for many web programs. If you were compiling your own mapserv.exe file, you install it by copying it into the cgi-bin folder. By default, this folder is located in the \ms4w\Apache\cgi-bin folder on the drive MS4W is installed on (e.g., C: orD:). There may be several versions of MapServer located there. For example, mapserv_36.exe is MapServer Version 3.6 (very out of date) and mapserv_44.exe is the most recent Version 4.4. Usually the more recent version will just be called mapserv.exe.

Preparing MapServer on Linux is also described in Chapter 4. Installing the MapServer CGI program is similar to how you do so for MS4W. The mapserv executable is simply copied (or linked) to Apache’s cgi-bin folder. For example, on SuSE Linux, the web server’s cgi-bin folder is located at /srv/www/cgi-bin. The mapserv application must be copied into this folder so it is accessible to the web server. These instructions also apply to non-MS4W installations of Apache on other platforms.

Configuring Apache to use MapServer doesn’t have to be complicated. If you put the mapserv/mapserv.exe program into the web server’s default cgi-bin location, there may not be much more to do to get the program running. The next section gives a couple of example tests to see if it is running properly.

There are other settings you will need in order to access maps produced by MapServer. When MapServer runs, it needs a temporary area to create the images for maps, legends, scale bars, etc. This temporary folder must also be accessible to the web so that users can view the images created by MapServer.

> chown wwwrun.www /srv/www/htdocs/ms_tmp

You can run a few tests to check that the MapServer program is properly set up. The set up of MS4W and Linux running Apache is very similar, but there are some differences worth mentioning.

No query information to decode. QUERY_STRING is set, but empty.

No query information to decode. QUERY_STRING is set, but empty.

To test that MapServer can actually create maps, you will build on the demonstration map files used with the command-line tools in Chapter 10.

The countries_simpl shapefile dataset can be downloaded as a compressed archive file from http://ftp.intevation.de/freegis/worlddata/freegis_worlddata-0.1_simpl.tar.gz.

The map file example from Chapter 10 will be customized further and made into a web-based application. To do so, there are three files involved:

Figure 11-1 illustrates how the basic application begins, with a start page sending settings to the CGI to produce a map.

Figure 11-1. The start page initializes MapServer by passing it a map file and an HTML template document

Example 11-1 takes the demonstration map file global.map, used in the previous chapter, and adds the settings required to make it a web map. The additional settings are highlighted.

MAP
  SIZE 600 300
  EXTENT -180 -90 180 90
  IMAGECOLOR 180 180 250

  UNITS DD

  SCALEBAR
    STATUS EMBED
    UNITS KILOMETERS
    INTERVALS 3
    TRANSPARENT TRUE
    OUTLINECOLOR 0 0 0
  END

  LEGEND
    STATUS EMBED
    POSITION LR
    TRANSPARENT TRUE
  END

  WEB
    TEMPLATE global.html
    IMAGEPATH "/srv/www/htdocs/tmp/"
    IMAGEURL "/tmp/"
 END

  LAYER
    NAME countries
    TYPE POLYGON
    STATUS DEFAULT
    DATA countries_simpl
    LABELITEM 'NAME'
   LABELMAXSCALE 50000000
    CLASSITEM 'NAME'
    CLASS
      NAME 'Bulgaria'
      EXPRESSION 'Bulgaria'
      OUTLINECOLOR 100 100 100
      COLOR 255 255 150
      LABEL
        SIZE LARGE
        OUTLINECOLOR 255 255 255
        MINFEATURESIZE 40
      END
    END
    CLASS
      NAME 'All Countries'
      EXPRESSION ('[NAME]' ne 'Bulgaria')
      OUTLINECOLOR 100 100 100
      COLOR 200 200 200
    END
  END
END

Only a few lines were added to make the map file work with the web server instead of command-line tools.

WEB
TEMPLATE global.html
IMAGEPATH "/ms4w/tmp/ms_tmp/"
IMAGEURL "/ms_tmp/"
END

A whole new object called WEB was added. There are three parts to the web object:

LABELMAXSCALE 50000000 was also added to the countries layer. This sets the map to show labels only when zoomed in to a certain map scale. The scale of the initial map is so small that Bulgaria is barely visible. Having a label on top of the country makes it harder to see; instead, as you zoom in to a more readable scale, the labels will appear.

With these map file settings in place, you can set up an initialization page. This page will be called index.html and its contents are listed in Example 11-2. The page can be called whatever you want.

<HTML>
<HEAD><TITLE>MapServer Test</TITLE></HEAD>
<CENTER><H2>MapServer Test</H2>

<FORM method=GET action="/cgi-bin/mapserv">
  <INPUT type="hidden" name="map" value="/srv/www/htdocs/global.map">
  <INPUT type="hidden" name="layer" value="countries">

  <INPUT type="hidden" name="zoomdir" value=1>
  <INPUT type="hidden" name="zoomsize" value=2>

  <INPUT type="hidden" name="program" value="/cgi-bin/mapserv">

  <INPUT type="submit" value="Start MapServer">
</FORM></CENTER></BODY></HTML>

This example is almost as stripped down as it can be. There is a title and heading on the page. Other than that, the rest of the HTML code is for starting MapServer. This page can be completely customized as long as the form and its variables are maintained.

All this page shows is a single button: Start MapServer. Behind the page are a bunch of hidden settings that are passed to MapServer when the form is submitted. This starts the first map. After the application is started, the index.html page isn’t used.

The MapServer CGI application sends the viewer a new web page. The URL to that web page contains several variables (like the ones defined in index.html). When a user requests a change to the map, it then sends those variables back to the CGI for reprocessing. The purpose of the index.html page is to get the whole process started without forcing you to have a complex-looking initial URL.

As you saw in Example 11-1, a template file called global.html is specified in the map file. This template file is also a web page written in HTML. MapServer takes this page and populates portions of it before sending it back to the user’s web browser. Example 11-3 shows my global.html code.

<HTML>
<HEAD><TITLE>MapServer Test</TITLE></HEAD>
<CENTER><H2>MapServer Test</H2>
<HR>

<FORM method=GET action="/cgi-bin/mapserv">
  <INPUT NAME="img" TYPE="image" SRC="[img]" width=600 height=300 border=0
               ALT="Map Image">

  <INPUT type=hidden name=zoomdir value=1 [zoomdir_1_check] >
  <INPUT type=hidden name=zoomsize size=4 value=[zoomsize]>

  <INPUT type="hidden" name="imgxy" value="[center_x] [center_y]">
  <INPUT type="hidden" name="imgext" value="[mapext]">
  <INPUT type="hidden" name="map" value="[map]">
  <INPUT type="hidden" name="savequery" value="true">
  <INPUT type="hidden" name="mapext" value="shapes">

</FORM></CENTER></BODY></HTML>

If you are familiar with HTML forms and tags, you may notice that the only objects visible on this page are the heading and title and an image. The image source (SRC) is filled in by MapServer in real time when the page is generated.

When MapServer populates global.html, it checks for any MapServer-specific variables, such as [img]. MapServer replaces this text with the URL to the map image on the web site. This is the temporary map image that MapServer created.

Figure 11-2 shows the output web page created by the global.html.

The map will look exactly like some of the map output from the command-line tools in Chapter 10. The only difference is that this map is being created by MapServer when requested, and automatically embedded into a web page.

The basic global.html template has virtually no controls, or at least none that are apparent. Controls refers to the buttons and check boxes you see on many web maps. These were deliberately left out so that this example would be simple to implement, and the HTML code wouldn’t be more confusing than necessary.

To interact with this map, just click on the map, and it will zoom in towards that location. Click once on the map, and then wait for the map to update. Once the image is updated, click again. Notice that if you zoom in toward Bulgaria, the label starts to appear. The results of clicking twice on the map are shown in Figure 11-3.

Because the number of controls has been kept to a minimum, there are no zoom-out buttons. In a web-mapping application this simple, the only way to zoom out is for

Figure 11-2. The basic global web map example

Figure 11-3. Zooming in to Bulgaria by clicking two times on the map

the user to go back in the web browser. This actually works reasonably intuitively because web page users are used to going back to previous pages.

If you’ve made it this far with your application, MapServer is set up and running well. Of course there are many other options and settings you can use. Some of these are covered in the next section when you start to make further customizations to the global map example.