Web Based Gis Applications Computer Science Essay

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The emergence of the Internet has had a ripple effect on the popularity of Web-GIS related websites which are also called Web Mapping sites - sites which embed some kind of geographical information system/mapping functionalities into them. They offer so many concepts which vary from being used as an Interactive Web Map or as a decision-support tool for urban & regional planners or people in the environmental industry. They are built from a variety of geographical information datasets, uploaded on a website and being used as a communication medium between the public and the developer/appropriate personnel to convey message across or to access information.

The massive growth of the Internet and availability of geographical information datasets has had an effect in an increase of demand for web mapping sites. Maps have graduated from paper maps/static maps on the web sites which only display still images to interactive and animated maps (Zaslavsky, 2000). Web Mapping site can be defined as one that uses the Internet as a medium to access and distribute geographic datasets for the purpose of visualization and to perform queries/analysis (Peng, n.d.)

Types of Web Mapping Architecture

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Hosting a web mapping site is not the core of the software development cycle but having a working infrastructure too is very crucial. This has been a hindrance over the years; being able to seamlessly integrate large GIS datasets over the web with a standard exchange mechanism for the geographical data.

The OpenGIS Consortium (OGS) has a standard for developers to conform to who want to deploy a webmap service through a server and hosted on a website (Marini et al., 2002). They are;

To produce a map whose elements would either be a picture, a set of geographical feature data - shapefiles, or some geographical elements.

Should be able to answer simple queries about the content of the map.

Communicate to the other programs its capabilities in terms of maps that can be produced and those which can be queried further

Also, the problem of a working infrastructure has been alleviated by OGS by making interoperability achievable with huge GIS datasets over the web. Web Map Server and Geographic Markup Language are such standards as viewed from (Shekhar et al., n.d.). Viewing traditional GIS data over the Internet requires the client computer to have some form of GIS Software installed on them but this is not efficient enough because it will be demanding lots of resources to have these software installed all over computers that will have to access this, the reason for better ways to inhibit different architecture that will enable GIS data to be downloaded by means of four major techniques which include GIS Java applets, GIS Active X Controls, Common Gateway Interface-based Internet GIS and GIS Plug-Ins as viewed from (Peng, n.d.). Two major architecture here are to be enumerated.

Clent-Side Internet GIS

Server Side Internet GIS (Thin Client)

Case Studies

Los Angeles Traffic Site http://losangeles.cbslocal.com/traffic/

This website looks at real traffic conditions in the city of Los Angeles, California, the United States of America. It allows commuters to log into a site and click on the area they intend to commute to, view life traffic conditions at these places.

Architecture Involved

The technology utilized here is called Server-Side Internet GIS. Here there is much reliance on the GIS Server to perform the analysis, generate the output and send it back to the user through the web browser. There is an intermediary here between the user and the GIS program which is called the Common Gateway Interface (CGI). The web browser is the front-end interface.

WWW

Server

(http)

WWW

Browser

CGI

Script

User Invoke

Request

Deliver Translate

Send

Variables Results Results

Return

Results

GIS

Server

Fig 1: Work process of Server Side Internet GIS using a Common Gateway Interface as viewed from (Peng, n.d.)

The User of the site accessed the website by typing the Uniform Resource Locator http://losangeles.cbslocal.com/traffic/

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The Web browser now interprets the URL and sends it to the Web Server.

The Web Server receives the request, decodes it into a path and file name

The web server points to a CGI (the CGI script is responsible for handshaking-communicating between the web server and the GIS Server)

The Web Server launches the GIS script for execution-in this case traffic situation where users click on a particular placemark on the thematic map shown in the website)

The CGI script now communicates with the GIS Server and translates the input from the user on the web browser to a format the GIS Server will be able to decode.

The GIS Server processes the request and generates an output like showing current traffic situation of a particular location that was clicked, showing route information/directions from one location to another; the former being in form of thematic maps and the latter in form of JPEG file.

Note: There will have to be lots of CCTV cameras installed at these locations within Los Angeles such that live traffic situations can be visualized from these places. They will have to be connected through some GIS-related Database Management Framework and uploaded to the GIS Server at regular intervals.

The GIS Server now transfers the output to the CGI script which in turn sends it to the web server and finally passes it on to the browser before the output is viewed by the user.

Advantages of this technology

The GIS Server does all the work here (all analysis are being performed here) so therefore the workload on the client side is negligible. All functionalities of the existing GIS Server software like ArcIMS, ArcInfo, ArcGIS are fully utilized.

Irrespective of the Operating System the User uses, this technology can be carried out

Disadvantages of this technology

The HTML code embedded in the web browser that is generated when a request is sent is static meaning that similar actions that have been generated previously cannot be remembered by the web server. This implies that the whole routine from Web Server to call the CGI Scripts and sending of variables to the GIS Server will have to be performed over and over again irrespective of whether similar actions have been previously parsed. This generates a lot of bandwidth on the Internet and makes the process to be slow because every operation has to be conducted by the GIS Server.

The CGI Script here handles all requests from the web browser to the GIS server and there is much pressure on it and it becomes difficult for it to process large amount of requests from users especially where several users across the Internet perform similar requests at the same time.

The Users cannot interact with the website and send their comments, click and draw an enclosed area, click on a location and send their traffic updates because of the limitations inherent in the web browser. They are only permitted to click on hyperlinks.

Easement Locator Tool Website (http://www.montgomeryplanning.org/environment/forest/easements/easement_tool.shtm)

This site is from the Montgomery Planning department from the County of Montgomery in the United States of America. The aim of the site is to provide a platform for users particularly within the state to report any form of violation on conservation easement sites (forest sites where any form of construction is prohibited). This site utilizes the client-side architecture because users can interact with it through means of map queries, submission of violations seen, searching for an address or owner of a location site and using of the identify tool.

Architecture Involved

As mentioned earlier, this site makes use of the client-side architecture. A diagram below shows the block through which this process is executed. It is also worthy to note here that the site makes use of java applets which are executable java programs (Peng, n.d.)

Fig 2: Framework of a Dynamic WebMap Service (Zhao et al., n.d.)

The Web browser (Firefox, Internet Explorer) allows the user to type the Uniform Resource Locator for the Montgomery Forest Conservation site http://www.montgomeryplanning.org/environment/forest/easements/easement_tool.shtm and then the request is sent to the web server to load the site.

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The web server now receives the request and sends the appropriate HTML file.

The web server now decodes the HTML file and locates the java applet tag

The java applet tag is downloaded from the WebGIS Server where it resides.

Other java server pages (JSP) and programs too are downloaded depending on the action that was invoked by the user (Peng, n.d.)

The applet is displayed on the browser or inside its own frame.

The steps just listed explain the upper tier of the diagram but the lower tier is what makes the client-side architecture have an edge over the server-side. The WebGIS server is responsible for establishing dynamic database connection that will facilitate the creation of a dynamic web map service and then return to the display on the web browser via the webserver.

The lower tier which consists of a dynamic database connection makes use of dynamic connection pool which registers some frequently database queries and functions that can be generated by the users of the site and puts them into memory so that when a similar action is performed, there is no need to establish a fresh connection and restart the server frequently before which the different data are got from different databases.

The shortcomings of this technique is that java applets cannot connect with other computers on the network apart from the one they were downloaded from and they can only be run on java enabled browsers.

City of Ekurhuleni, South Africa http://gis.ekurhuleni.gov.za/

This site enables users to access map for the citizens of Ekurhuleni in South Africa. Queries can be performed on the site and data downloaded too. It follows the same procedure as the client-side architecture for the Montgomery Easement locator site explained earlier.

Conclusion

Web Map sites are rapidly evolving. It is the wave of the future. Some authors have their views and encounter problems that arise from interoperability, initial design and implementation of GIS capabilities over the Internet (Anselin et al.,2004). The GIS software too is a major problem (both cost of procurement and training provided) as said by (Fonseca et al.,2006). Nevertheless, Web Based GIS tools have stamped their authority in the marketplace today and they are everywhere we go from hand-held devices to interactive online web maps. They make our lives easier particularly in terms of navigation.