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Generating online map for Skudai using the Minnesota Map Server
4. Skudai Online Map Implementation
To generate the Skudai online map, a common approach is to construct two components, namely, (a) GIS database component, and (b) web component. 4.1 GIS database component Internet based geographic data services involve spatial and non-spatial (attribute) data management (Honda et al, 2002). The construction of GIS database component includes data collection, data processing and database design. Indeed, a GIS database requires good design in order to manage data structure in the database. Figure 2 illustrates the entire process of GIS database management for this project.  Figure 2. GIS database development. The spatial data that acquired from the Jabatan Perancangan Bandar dan Desa (JPBD) is in DXF format. Data editing need to be done in order to ensure the completeness of the data that is by using AutoCAD MAP 2000i. The data then converted into coverage for the typical data processing like clean, build topology and projection by using available tools in ArcToolBox of ArcGIS 8.1. Finally, the data (in shape file) is exported to ArcView 3.1 for attribute data. 4.2 Web component The homepage of this project is a web interface that enables online access to the online map. It is a typical HTML page that contains the link to the Skudai online map as well as links to the Minnesota Map Server, University Technology Malaysia and MPJBT homepages. We developed the homepage by using the Microsoft FrontPage 2002. Figure 3 shows the structure of the homepage and Figure 4 shows the homepage of Skudai online map with the following URL address: http://beh/SKUDAI/MAINPAGE.htm. Once the homepage is developed, then next step is to implement the online map. Initially the MapServer CGI program (mapserv.exe) needs to be installed and can be downloaded from the Minnesota map server homepage. The installation itself takes a two-step process. Firstly, the program needs to be placed under the web accessible directory. For IIS, Inetpub is a web accessible directory and the program is installed in Scripts, which is a sub- directory of Inetpub (e.g. d:\Inetpub\Scipts). Secondly, the ‘espg’ file is placed into the created PROJ folder. This file is needed for the map projection definition.  Figure 3. The structure of homepage.  Figure 4. The homepage of Skudai online map Besides the Mapserv program, the Minnesota Map Server application requests GIS data and MapServer-specific files, namely, Map file and HTML template files. It is important to place them properly in the web accessible directory. Error will appear easily if the files are in the wrong path. Figure 5 illustrates the directory structure of the online map. In this case, the folder name of the Skudai online map is “teskSk” and it is stored in the Scripts subdirectory. Apart from that, a “tmp” folder is also created in the Script subdirectory that stores output files from the map server. The folder must allow web users to write on it.  Figure 5. The directory structure of the online map. As the GIS data is stored in the “testSk” folder, it needs to be defined in the MapServer-specific file, namely, the Map file. In fact, this file defines every object for the online map, including data layer, scalebar, map, legend, projection and web object. The objective of object definition is to define how the map will look like and be presented. Here some cartographic aspects need to be considered by the developer. The definition of each object is different and some examples are illustrated in Figure 6.  Figure 6. Examples of object definition. The defined objects such as map, legend and scalebar are presented on the online map interface. But, the Map file is not used for the designing of the interface, the Template files are used instead. The template files are used for the following tasks, namely, designing the interface, generating mapping tools and conducting query. HTML code is the common stuffs in the Template files (i.e. for designing the interface). Besides HTML code, the Minnesota map server also supports other programming languages such as JavaScript for generating mapping tools. To conduct query with the Template file, every layer is required to have a particular template file. This template file comprises attribute table and perhaps the query map display. The attribute table contains columns that carry the same as the columns in the DBF file. In addition, the path of the template file is also determined in the Map file. Consequently, the template file can be linked to the DBF file for the attributes data retrieval purposes. Both Map file and Template file are developed and edited using Notepad. Web browser such as Internet Explorer or Netscape Communicator could be used to compile the files and view the results. The Skudai online map is presented in Figure 7.  Figure 7. Skudai online map. |