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
•OpenStreetMap
•WikiMapia
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.
AN ARCHITECTURE OF AN OVERALL WEBGIS
SYSTEM
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
01.CLIENT
SERVER 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
02.
DISTRIBUTED ARCHITECTURE
Client
server architecture
q Two
types of client server architecture
A. Thin
client architecture
B.
Thick client architecture
THIN
CLINT ARCHITECTURE
THICK
CLIENT ARCHITECTURE
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