Geographic Information System in a web enabled world is what Asima Mishra discusses here

Geographic Information System (GIS) is a computer-assisted system for the acquisition, storage, analysis and display of geographic data. Like any other information system, GIS is also primarily an input-output system and includes DBMS functions. It is different from conventional DBMS and Information Systems in the sense that every piece of information has to be directly or indirectly associated with location on earth’s surface expressed as co-ordinates with respect to any co-ordinate system.

The explosion of Internet activity over recent years has sparked a global move away from traditional isolated single-software, single-machine computing, towards distributed multiple-software, multiple-machine computing. The World Wide Web has great potential as an interface into Geographic Information Systems and services. The growing demand of geographic services including real-time mapping, interactive world map generation and other environmental data analysis, requires procession of huge amount of spatial data. The development of on-line geographic services includes preservation of state, image generation and conversion techniques, image caching and data formats. The future of on-line GIS looks promising with new techniques such as client-side processing and new standards and protocols.

Need for Web GIS

The traditional model for a GIS assumes that the system consists of a single software package, plus data, on a single machine. This model no longer meets the realities of many GIS projects, which today are often multi-agency, multi-disciplinary, multi-platform, and multi-software. Large numbers of contributors may be involved, and there may be a large pool of potential users. These users may require not only maps, but also many forms of outputs like documents and charts. Moreover they are likely to require access to the most current data available and not the copies that may be months, or even years, old. A central practical issue, therefore is how to provide widespread, device-independent, access to a GIS for large numbers of contributors and users.

The obvious solution is remote access to GIS via computer networks. i.e. the Internet. More specifically, the World Wide Web provides an ideal platform-independent, multi-media communi-cations medium. Here we address the viability, development and future of on-line geographic information services. New protocols on the Internet provide an ideal environment for networking GIS. Most promising is the Hyper Text Transfer Protocol (HTTP), which is a generic hypertext/multimedia communications protocol. HTTP provided by the World Wide Web is fast becoming the medium of choice for on-line publishing of all kinds. The advantages of the World Wide Web are that generic browsing software (such as Netscape) makes it essentially device-independent. Also hypertext links across the network make it possible to integrate many different services in completely seamless fashion. Given the increasing use of the internet for on-line information exchange, it is therefore timely to consider how to develop and use GIS via the Internet.

Advantages of Web GIS

The traditional standalone GIS has been used extensively by the government agencies and institutions for spatial analysis and natural resource management. These informations are used by the respective nodal bodies but are not properly disseminated for use of general public as and when required. The recent trend shows a significant growth in the use of World Wide Web and Internet technologies to place a geographical data ubiquitously on the desktop and draw data from a wide variety of sources only to be used by the public quickly and efficiently. Enterprise wise GIS requires building of methodologies to make the data available to all users. Web became the ideal medium to share information. Thus evolved the Web based GIS, and administering the information at government level gave rise to electronic governance.

There are lots of advantages of WEB based GIS. With this technology we can have centralised base-map data which are large enough to be on individual systems. When the GIS data is centralized it can be managed more easily and everyone has access to changes as soon as they are updated. Individuals need only standard Web Servers to run the application.

Infrastructure and Methodology

The web based GIS software mainly consists of two components: the server and web client, which run the browser. The server is a set of applications that serves the request of the clients. The web client is the general user who performs an information retrieval operation, the server identifies user by logging into the system. The server validates and lists all projects meant for information display. The user can select a project and start working on the spatial and non-spatial data associated with the project. There are two basic approaches to implement GIS in the web i.e. server-side applications and client-side applications

Server-Side Applications

An Internet GIS server usually combines a standard Web (HTTP) server and a GIS application server. Here all the complex and proprietary softwares as well as the GIS databases reside on a server that’s administered by the deploying organization. Having applications centralized on one or a few machines significantly simplifies development, deployment and maintenance. The Web server passes the request to a GIS application server which runs an address-matching routine, generates a map graphic, converts the graphic to Web format, wraps the image in HTML and sends it back to the Web server which then returns the response to the client as a standard Web page.

Disadvantages of server-side solutions are primarily associated with limited user interface and poor performance. In GIS, there are many applications in which users need to drag windows or select multiple features before an action takes place. It’s difficult or impossible to do this using a standard Web interface. In addition, server-side applications must retrieve all the application information from the server for every operation. When users reset a display window by panning or zooming, turn a layer on or off, or take any other action, the request must be sent to the server and returned. This results in many requests, which can cause poor performance.

Client-Side Applications

In client-side Internet GIS, the client is enhanced to support GIS operations. Some systems move a substantial amount of GIS functionality to the client, and some only enhance the user interface slightly. Client-side solutions typically are implemented by augmenting the Web browser with Java, ActiveX or plug-ins. However, some client-side solutions require users to install a complete client application. But to implement client-side solutions of any kind, software must be transferred to users.

The primary advantages of client-side solutions are the abilities to enhance user interfaces, improve performance and implement solutions using vector data. Client-side solutions can be implemented with all the features and capabilities allowed by a modern GUI. Multipoint feature selection, selecting an area by dragging a window and modal cursor operations controlled by clicking on menu icons are capabilities available in client-side products that aren’t available in server-side implementations.

When client-side solutions use vector data structures, a large set of graphic and GIS operations can be performed locally. Window display changes can happen without re-transmitting a request to the server. Core GIS operations like editing, buffering, overlay analysis and route tracing are examples of operations that are enhanced by exploiting vector data structures on the client side.

The disadvantages associated with client-side solutions relate to distributing software and data. By definition, when companies implement client-side Internet GIS, they must somehow distribute software to users. Due to platform incompatibilities otherwise users will face problem.

Web based GIS can be implemented to each and every user sector where mapping is an indispensable part. In this case spatial as well as non-spatial data can be made available to everyone efficiently and economically.

Asima Mishra, MTS, Geomatics Group
is currently working in geomatics application programming and GIS training.
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