Geog 258: Maps and GIS

Geog 258

March 6, 2006

Maps and GIS go online

Table of content

Distributed GIS: architecture

Distributing maps

Distributing geodata

Impact of internet

Internet is changing the way we retrieve maps or do a GIS

· Input: we acquire data from the internet

· Operation: some internet provide GIServices (e.g. Mapquest, geocoding service)

· Output: now people publish the result of their analysis on the internet

Distributed GIS?

“Network-based geographic information services that utilize both wired and wireless internet to access geographic information, spatial analytical tools, and GIS web services” (Peng and Tsou 2003)

Evolution of GIS architecture

From centralized GISystems to distributed GIServices

Mainframe GIS: GIS on mainframe (early 1980~)

Desktop GIS: GIS on the personal computer (early 1990~) e.g. your lab work

Internet GIS: GIS on the wired network environment (mid 1990~) e.g. mapquest

Mobile GIS: GIS on the wireless device (later 1990~) e.g. location-based service

Fundamentals of Distributed GIS architecture

Typical application has three elements: Presentation, Logic, Data

where presentation represents user interface while logic (a.k.a. business logic) refers to processing.

Three elements can be “functionally” (not physically) seen as either client or server depending on which makes a request (=client) and which fulfills the request (=server)

Client/server architecture

If the three elements reside in the same personal computer, the application would be a stand-alone one. If the three elements reside in different machines, the application is called a client/server application. A web application is example of client/server model implementation (web browser as the client).

Middleware

In order for the client to communicate with the server, we need translator to link them together. This intermediate connection component is called middleware.

(e.g. TCP/IP, RPC, DCOM, CORBA)

Partitioning point

Three application elements can be divided into client and server at any point (a to e).

e

d

a

The system whose partitioning point is closer to a is said to have a thin client

The system whose partitioning point is closer to e is said to have a thick client

Distributed-Component Framework

In object-oriented modeling, application can be seen as being composed of components that can interoperate across language. (e.g. COM)

Distributed component framework breaks up the client and server sides of an application into components interoperable across operating systems, networks, and hardware. (e.g. DCOM, CORBA, .NET, Java Platform)

Three types of GIS architecture

· Traditional GISystems: closed and centralized systems

· Client/Server GISystems: based on C/S architecture

· Distributed GIServices: built upon distributed-component technology; open and distributed system

Publishing maps on the internet (Web Mapping)

Web mapping can be classified into four categories.

More interaction between users and applications, and higher level of functionalities if you go to the right in the figure above.

1. Client/Server

1.1 Server-side strategy

More of functionalities are placed in the server side; i.e. thin client

1) Static map publishing: web C/S with thin client

Image-embedded HTML, No interaction with users is allowed

2) Static web mapping: web C/S with medium client

Server processes data, and client (web browser) serves as the window to show the result returned from server

e.g. Xerox Map View, Alexandria Digital Library

1.2 Client-side strategy

More of functionalities are placed in the client side; i.e. thick client

3) Interactive web mapping: web C/S with thick client

Client (your personal computer) downloads program (such as plug-in, DHML View, Java Applet, ActiveX) from the server, and perform operation in the client

2. Distributed

4) Distributed GIServices: distributed-component technology

Internet mapping systems shown above do not interoperate with each other (i.e. flatform-dependent). Distributed GIServices built upon distributed-component technology is more scalable and interoperable.

Try American fact finder

Try this for searching web mapping sites

http://www.gis.com/showcase/trygis/search.cfm

Distributing the data on the internet

Interntet has had a tremendous impact on the accessibility of GIS data, and on the ability of GIS users to share datasets

Datasets are available in different levels from object to collection

1) Object-Level Metadata

e.g. National Atlas of the United Stated

Data comes along with FGDC-compliant metadat

2) Geolibraries

Digital libraries that can be searched for information about any user-defined geographic location, provides electronic catalog

e.g. Alexandria Digital Library http://alexandria.sdc.ucsb.edu/