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As defined by Dyson, generally the Internet is a massive networking infrastructure that globally links millions of computers together. This facilitates the communication between any 2 or more computer as long as they are all connected to the Internet using the Transmission Control Protocol/Internet Protocol (TCP/IP).
The World Wide Web is a way of sharing and accessing information through the internet. The Web uses the Hyper Text Transfer Protocol (HTTP) to transmit data over the internet. The HTTP essentially provides a mechanism whereby a client requests a document and a server sends that document. Services using HTTP to allow applications to communicate to exchange business logic use the Web to share information (Weinberger 2002).
Web GIS refers to developing GIS functionality in the Internet, Worldwide Web, and private intranets. Web GIS is capable of distributing geographic information to a very large worldwide audience which means that users of the internet access GIS applications from their browsers without having to buy commercial GIS software (Kenneth and Kirvan 1997). As mentioned previously, the OGC protocols like Web Map Services (WMS) and Web Feature Services (WFS) have made it possible to distribute geographical information via the web. The main challenge of Web GIS is the development of software systems that are platform independent and can run on any computer connected to the Internet (or any TCP/IP-based network) supporting a Web browser. This is a revolution to the traditional way of operating commercial GIS software over local-area networks (LANs) or intranets on just a few types of computer hardware. There are 3 approaches used to add GIS functionality to the Web. The Server-side allows users (clients) to submit requests for data and analysis to a Web server. The Web server then processes the requests and responds by returning data to the client. Client-side allows the users to perform some data manipulation and analysis locally on their own machines. Hybrid strategies or the Client-Server approach is where the Client and Server processes can be combined to maximize performance and meet special user needs (Tereshenkov 2009). Developers of Web GIS can program their applications from scratch or they can now, as in most cases, purchase the necessary GIS modules from commercial vendors. Some of the advantages of Web Based GIS to government authorities include: sharing of data by the departments, centralized data storage and management, services are joined-up and the holistic view of data to ensure holistic decision making.
Web GIS Architecture
Generally there are two main types of Web GIS Architecture: the two tier client server architecture and the three tier client server architecture. The two tier architecture is made up of the client side software and the server side software. When there is a communication protocol between the client and server, this on-set the transfer of spatial data from server to client where the client software facilitates visualization of spatial data while the server software only offers database service (Luqun et al., 2002). The three tier client server architecture comprises three different logical levels. The first level is the user interface (client). The second level is the business logic level which does the GIS transaction processing. The third level is the GIS data storage service which is responsible for the continuous storage of functional data. The Client side comprises the web browser e.g. Firefox or Internet Explorer. The business logic usually is made up of the HTTP Server or Web Server e.g. Apache and the Application Server or Map Server e.g. ArcGIS Server or Geoserver. The data tier can be made up of Database Management System (DBMS) Server e.g. PostgreSQL or SQL Server. According to Peng 2001, the three tier architecture has 3 main advantages: better performance, scalability and security.
Client Side Applications
Web GIS Application Development Cycle
The application development cycle can be said to be organization and project specific however in terms of a Web GIS, the following diagram shows a well detailed model according to Allesheikh et al., 2002 that can be easily adopted.
Source: Allesheikh et al., 2002
Figure 4 Web GIS Development Cycle
The requirement analysis can be done through surveys with the users to determine user desired functionality, data layers, data attributes, user skills and spatial literacy. Based on the results of the requirement analysis, the conceptual design is drawn up which is basically the data model that identifies the entities and their relationships. Identification of suitable software to use is vital in the successful implementation of any web development process. Software can be evaluated for functionality, performance and cost. Web GIS involves the transfer of huge volumes of data hence issues of bandwidth and internet connection speed is important. The database design and construction phase is when the actual logical and physical design of the database is drawn up. Upon completion of the database design and construction, the necessary software and hardware identified will be purchased or sourced. The next step is to integrate the different components of the hardware and software and to test them to ensure they work as expected. Upon successful hardware/software system integration, the Web GIS application is then developed. The complexity of this phase is dependent upon the user desired functionality as specified in the requirement analysis phase. The final stage is to test the application to make sure it works as envisaged before releasing to the users.