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What is web GIS?

Web GIS is a type of distributed information system, comprising at least a server and a client, where the server is a GIS server and the client is a web browser, desktop application, or mobile application. In its simplest form, web GIS can be defined as any GIS that uses web technology to communicate between a server and a client.
Here are a few key elements essential to web GIS:
The server has a URL so that clients can find it on the web.
The client relies on HTTP specifications to send requests to the server.
The server performs the requested GIS operations and sends responses to the client via HTTP.
The format of the response sent to the client can be in many formats, such as HTML, binary image, XML (Extensible Markup Language), or JSON (JavaScript Object Notation).
The web GIS advantage

By utilizing the Internet to access information over the web without regard to how far apart the server and client might be from each other, web GIS introduces distinct advantages over traditional desktop GIS, including the following:
01. A global reach:
02. A large number of users:
03. Better cross-platform capability:
04. Low cost as averaged by the number of users:
05. Easy to use:
06. Unified updates:
Disadvantage of web gis

01.Reliability issues
02. Geodata is expensive
03. Bandwidth issues
04. Limited screen space
05. Complex to develop
06.  Immature development tools
07. Copyright issues
08. Privacy issues
Types of web maps

A first classification of web maps has been made by Kraak in 2001.He distinguished static and dynamic web maps and further distinguished interactive and view only web maps. Today there an increased number of dynamic web maps types, and static web map sources.
01. Analytical web maps
Analytical web maps offer GIS analysis. The geodata can be a static provision, or needs updates. The borderline between analytical web maps and web GIS is fuzzy. Parts of the analysis can be carried out by the GIS geodata server. As web clients gain capabilities processing is distributed.
02. Animated and realtime
Realtime maps show the situation of a phenomenon in close to real-time (only a few seconds or minutes delay). They are usually animated. Data is collected by sensors and the maps are generated or updated at regular intervals or on demand.
03. Collaborative web maps
Collaborative maps are a developing potential . In proprietary or open source collaborative software, users collaborate to create and improve the web mapping experience. Some collaborative web mapping projects are:
Google Map Maker
Here Map Creator
04. Online atlases
The traditional atlas goes through a remarkably large transition when hosted on the web. Atlases can cease their printed editions or offer printing on demand. Some atlases also offer raw data downloads of the underlying geospatial data sources.
05. Static web maps
Static web pages are view only without animation or interactivity. These files are created once, often manually, and infrequently updated. Typical graphics formats for static web maps are PNG, JPEG, GIF, or TIFF (e.g., drg) for raster files, SVG, PDF or SWF for vector files. These include scanned paper maps not designed as screen maps. Paper maps have a much higher resolution and information density than typical computer displays of the same physical size, and might be unreadable when displayed on screens at the wrong resolution.

To identify subsystems of an overall WebGIS we started from a general assumption that
geoinformation related to some area (i.e. city) cannot be captured, stored and maintained in a single
organizational unit GIS. Some of this information can have mutual and public importance, so it
should be shared and be accessible over Web.
Suggested architecture relies on a client/server model. A subsystem that acts as a client that enables
access to geoinformation is a WebGIS portal, while the function of sharing (role of a server) is
realized by expanding traditional GISs with a WMS and a WFS Web interfaces (Web-enabled GIS).
Using of OGC WMS and WFS interfaces for building WebGIS systems can be also found in
(Korduan and Bill, 2004). Figure 1 illustrates interrelation between components that correspond to subsystems.
                                 fig- Schematic view of an overall WebGIS architecture

 Typical three tire Architecture                                     
                          01.Presentation tire
                                -contains user interface
                          02. Application logic tire
                                - model & process GIS data
                          03. Storage tire
                                - Databases that store GIS data
                                          Client server architecture
Two types of client server  architecture
   A. Thin client architecture
   B.  Thick client architecture

                                                           THIN CLINT ARCHITECTURE
                                                           THICK CLIENT ARCHITECTURE

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