Distributed GIS

Distributed GIS concerns itself with Geograpical Information Systems that do not have all of the system components in the same physical location. This could be the processing, the database, the rendering or the user interface. Examples of distributed systems are web-based GIS, Mobile GIS, Corporate GIS and GRID computing. .

Corporate GIS
A corporate Geographical Information System, is similar to Enterprise GIS (see below) and satisfies the spatial information needs of an organisation as a whole in an integrated manner. Corporate GIS consists of four technological elements which are data, standards, information technology and personnel with expertise. It is a coordinated approach that moves away from fragmented desktop GIS. The design of a corporate GIS includes the construction of a centralised corporate database that is designed to be the principle resource for an entire organisation. The corporate database is specifically designed to efficiently and effectively suit the requirements of the organisation. Essential to a corporate GIS is the effective management of the corporate database and the establishment of standards such as OGC for mapping and database technologies.

Benefits
There are many advantages of a corporate GIS. Firstly, all the users in the organisation have access to shared, complete, accurate, high quality and up-to-date data. All the users in the organisation also have access to shared technology and people with expertise. Consequently, this improves the efficiency and effectiveness of the organisation as a whole. A successfully managed corporate database reduces redundant collection and storage of information across the organisation. By centralising resources and efforts, it reduces the overall cost.

Recommended use
A corporate GIS is recommended for anyone from local governments to global governmental organisations. This is particularly useful if data is to be shared between governmental departments or organisations. However, a corporate GIS is considered not to be cost efficient for smaller organisations as it is expensive to implement.

Mobile GIS
Mobile GIS is the expansion of a Geographic Information System from the office into the field. This is heavily reliant upon wireless technologies to access remotely stored data. Mobile GIS may be based on toughened laptops or tablet PCs and have all or some of the functions of a desktop GIS. There are smaller PDA-based systems, which have a more limited but often tailored set of functions. They allow the capture, manipulation and storage of data in remote locations. This has the advantage of real time updating of central databases, thus removing the need for storage of multiple copies of data and lessening data replication.

Those that are reliant on real time data transfer are generally dependent upon the GSM networks and are limited to the bandwidths of these networks.

Device Limitations
Although not all applications of mobile GIS are limited by the device, many are. These limitations are more applicable to smaller devices such as cell phones and PDAs. Such devices have:
 * small screens with a limited resolution
 * limited memory and processing power
 * a limited (or no) keyboard
 * short battery life
 * are dependent upon a wireless signal
 * are more vulnerable to damage because of their mobility and use in field work

Enterprise GIS
Enterprise GIS refers to a geographical information system that integrates geographic data across multiple departments and serves the whole organisation. The basic idea of an enterprise GIS is to deal with departmental needs collectively instead of individually. When organisations started using GIS in the 1960s and 1970s, the focus was on individual projects where individual users created and maintained data sets on their own desktop computers. Due to extensive interaction and work-flow between departments, many organisations have in recent years switched from independent, stand-alone GIS systems to more integrated approaches that share resources and applications.

Some of the potential benefits that an enterprise GIS can provide include significantly reduced redundancy of data across the system, improved accuracy and integrity of geographic information, and more efficient use and sharing of data. Since data is one of the most significant investments in any GIS program, any approach that reduces acquisition costs while maintaining data quality is important. The implementation of an enterprise GIS may also reduce the overall GIS maintenance and support costs providing a more effective use of departmental GIS resources. Data can be integrated and used in decision making processes across the whole organisation.

Strategy
The development of the European Union (EU) ’’’INSPIRE’’’ initiative indicates this is a matter that is gaining more awareness at the national and EU scale. This states that there is a need to create ‘quality geo-referenced information’ that would be useful for a better understanding of human activities on environmental processes. Therefore it is an ambitious project that aims to develop a European spatial information database.

The GI strategy for Scotland was introduced in 2005 to provide a sustainable SDI, through the ’’One Scotland – One Geography’’ implementation plan. This documentation notes that it should be able to provide linkages to the ’’Spaces, Faces and Places of Scotland’’.

Although plans for a GI strategy have been in existence for some time, it was revealed at the AGI Scotland 2007 conference that a recent budget review by the Scottish Government indicated there will not be an allocation of resources to fund this initiative within the next term. Therefore a business plan will need to be presented in order to outline the cost-benefits involved with taking up the strategy.

Standards
The main standards for Distributed GIS are provided by the Open Geospatial Consortium (OGC). OGC is a non-profit international group which seeks to Web-Enable GIS and in turn Geo-Enable the web. One of the major issues concerning distributed GIS is the interoperability of the data since it can come in different formats using different projection systems. OGC standards seek to provide interoperability between data and to integrate existing data.

OGC
In terms of interoperability, the use of communication standards in Distributed GIS is particularly important. General standards for Geospatial Data have been developed by the Open Geospatial Consortium (OGC). For the exchange of Geospatial Data over the web, the most important OGC standards are Web Map Service (WMS) and Web Feature Service (WFS).

Using OGC compliant gateways allows for building very flexible Distributed GI Systems. Unlike monolithic GI Systems, OGC compliant systems are naturally web-based and do not have strict definitions of servers and clients. For instance, if a user (client) accesses a server, that server itself can act as a client of a number of further servers in order to retrieve data requested by the user. This concept allows for data retrieval from any number of different sources, providing consistent data standards are used.

Furthermore, this concept allows data transfer with systems not capable of GIS functionality. A key function of standards is the integration of different systems already existing and thus geo-enabling the web. Web services providing different functionality can be used simultaneously to combine data from different sources (mash-ups). Thus, different services on distributed servers can be combined for ‘service-chaining’ in order to add additional value to existing services. Providing a wide use of OGC standards by different web services, sharing distributed data of multiple organisations becomes possible.

Other standards
Some important languages used in OGC compliant systems are described in the following. XML stands for eXtensible Markup language and is widely used for displaying and interpreting data from computers. Thus the development of a web-based GI system requires several useful XML encodings that can effectively describe two-dimensional graphics such as maps SVG and at the same time store and transfer simple features GML. Because GML and SVG are both XML encodings, it is very straightforward to convert between the two using an XML Style Language Transformation XSLT. This gives an application a means of rendering GML, and in fact is the primary way that it has been accomplished among existing applications today. XML can introduce innovative web services, in terms of GIS. It allows geographic information to be easily translated in graphic and in these terms scalar vector graphics (SVG) can produce high quality dynamic outputs by using data retrieved from spatial databases. In the same aspect Google, one of the pioneers in web-based GIS, has developed its own language which also uses a XML structure. Keyhole Markup Language or KML is a file format used to display geographic data in an earth browser, such as Google Earth, Google Maps, and Google Maps for mobile browsers.

Global System for Mobile Communications
It is a global standard for mobile phones around the world. Networks using the GSM system offer transmission of voice, data and messages in text and multimedia form and provide web, telenet, ftp, email services etc. over the mobile network. Almost two million people are now using GSM. Five main standards of GSM exist: GSM 400, GSM 850, GSM 900, GSM-1800 (DCS) and GSM1900 (PCS). GSM 850 and GSM 1900 is used in North America, parts of Latin America and parts of Africa. In Europe, Asia and Australia GSM 900/1800 standard is used.

GSM consists of two components: the mobile radio telephone and Subscriber Identity Module. GSM is a cellular network, which is a radio network made up of a number of cells. For each cell, the transmitter (known as a base station) is transmitting and receiving signals. The base station is controlled through the Base Station Controller via the Mobile Switching Centre.

For GSM enhancement GPRS and UMTS technology was introduced. General Packet Radio Service is a packet-oriented data service for data transmission. Universal Mobile Telecommunications System is the Third Generation (3G) mobile communication system. Both provide similar services to 2G, but with greater bandwidth and speed.

Wireless Application Protocol (WAP)
Wireless Application Protocol is a standard for the data transmission of internet content and services. It is a secure specification that allows users to access the information instantly via mobile phones, pagers, two-way radios, smartphones and communicators. WAP supports HTML, XML, and Wireless Markup Language (WML), and is specifically designed for small screens and one-hand navigation without a keyboard. WML is scalable from two-line text displays up to the graphical screens found on smart phones. It is much stricter than HTML and is similar to JavaScript.

Location Based Services
Location Based Services (LBS) are services that are distributed wirelessly and provide information relevant to the user’s current location. These services include such things as ‘find my nearest …’, directions, and various vehicle monitoring systems, such as the GM OnStar system amongst others. Location based services are generally run on mobile phones and PDAs, and are intended for use by the general public more than Mobile GIS systems which are geared towards commercial enterprise. Devices can be located by triangulation using the mobile phone network and/or GPS.

Device limitations are similar to those for mobile GIS. In addition, any devices that are reliant on WAP will be limited by WAP functionality.

HTML
HTML, an initialism of Hypertext Markup Language, is the predominant markup language for web pages. It provides a means to describe the structure of text-based information in a document — by denoting certain text as headings, paragraphs, lists, and so on — and to supplement that text with interactive forms, embedded images, and other objects. HTML is written in the form of labels (known as tags), surrounded by angle brackets. HTML can also describe, to some degree, the appearance and semantics of a document, and can include embedded scripting language code which can affect the behavior of web browsers and other HTML processors.

HTML is also often used to refer to content of the MIME type text/html or even more broadly as a generic term for HTML whether in its XML-descended form (such as XHTML 1.0 and later) or its form descended directly from SGML (such as HTML 4.01 and earlier).

Scripting
An example of a scripting language is Perl. Perl is a general-purpose programming language originally developed for text manipulation and now used for a wide range of tasks including system administration, Web development, network programming, GUI development, and more.

The language is intended to be practical (easy to use, efficient, complete) rather than beautiful (tiny, elegant, minimal). Its major features include support for multiple programming paradigms (procedural, object-oriented, and functional styles), automatic memory management, built-in support for text processing, and a large collection of third-party modules.

Geotagging
Geotagging is the process of adding geographical identification metadata to resources such as websites, RSS feeds, images or videos. The metadata usually consist of latitude and longitude coordinates but may also include altitude, camera holding direction, place information and so on. The Flickr website is one of the more well-known Web services which host photos and provides functionality to add latitude and longitude information to the picture.

The main idea is to use metadata related to pictures and photo collection. A geotag is simply a properly-formed XML tag giving the geographic coordinates of a place. The coordinates can be specified in latitude and longitude or in UTM (Universal Transverse Mercator) coordinates. The RDFIG Geo vocabulary from the W3C is the common basis for the recommendations. It supplies official global names for the latitude, longitude, and altitude properties. These are given in a system of coordinates known as "the WGS84 datum". (A geographic datum specifies an ellipsoidal approximation to the Earth's surface; WGS84 is the most commonly used such datum for GPS).

To specify that the longitude of something is X, that its latitude is Y, and, optionally, that its altitude is Z, the form of the tags used is: Altitude is specified in meters. The prefix "geo:" represents the RDFIG Geo namespace, whose URL is:  http://www.w3.org/2003/01/geo/wgs84_pos# 

Geotagging an HTML element
The following tag will pass muster as correct XML in the context of XHTML (the newer dialect of HTML that adheres to the XML standard), but will also work in earlier HTML dialects, in the sense of being tolerated by all modern browsers. To geotag an HTML element, include a span of the following form:

If the geo namespace is defined at an outer level of the document, the namespace definition in the span tag can be omitted, leaving: 46.1124 In earlier HTML dialects, omitting the namespace definition is also appropriate, since the objective of adhering to the XML standard is irrelevant. This technique can be used to geotag a post in a weblog, or elements within any HTML document.

Geotagging XML (including RSS and RDF)
In XML simply include elements of the form:

as children of the element you wish to tag, and place the definition of the geo namespace at the outermost level of the document (or at the level you prefer).

Geotagging a web page
The following method is used to assign a location to a web page as a whole, rather than to its parts. In the element, include metatags of the form: In XHTML, the document namespace definition should include the geo tag. This form of meta tag follows the W3C recommendations.

Mashups
In distributed GIS, the term mashup refers to a generic web service which combines content and functionality from disparate sources; mashups reflect a separation of information and presentation. Mashups are increasingly being used in commercial and government applications as well as in the public domain.

When used in GIS, it reflects the concept of connecting your application with a mapping service (e.g., combining Google Maps with Chicago crime statistics to create Chicago crime statistics maps).

Mashups are fast, provide value for money and remove responsibility for the data from the creator.

Second generation systems provide mashups mainly based on URL parameters, while third generation systems (e.g., Google Maps) allow customisation via script (e.g., JavaScript).

Web Mapping Services
A web mapping service is a means of displaying and interacting with maps on the Web. The first web mapping service was the Xerox PARC Map Viewer built in 1993 and decommissioned in 2000.

There have been 3 generations of Web map service. The first generation was from 1993 onwards and consisted of simple image maps which had a single click function. The second generation was from 1996 onwards and still used image maps the one click function. However, they also had zoom and pan capabilities (although slow) and could be customised through the use of the URL API. The third generation was from 1998 onwards and were the first to include slippy maps. They utilise AJAX technology which enables seamless panning and zooming. They are customisable using the URL API and can have extended functionality programmed in using the DOM.

Web map services are based on the concept of the image map, whereby this defines the area overlaying an image (e.g. GIF). An image map can be processed client or server side. As functionality is built into the web server, performance is good. Image maps can be dynamic. When image maps are used for geographic purposes, the co-ordinate system must be transformed to the geographical origin to conform to the geographical standard of having the origin at the bottom left corner.

Web maps are used for location based services.

Examples of web mapping services are:
 * Streetmaps
 * Google Maps
 * Multimap
 * Bing Maps

Web 2.0
The Internet has gone far beyond the average person's thinking. It is not only chatting or just surfing the web but it is a new way of connecting people and how to bring the experience from a desktop to the browser which will be more user friendly. For this reason some Rich Internet Applications (RIA) are required.

Ajax is one of the widely used terms in this context in conjunction with Flash, Flex and Nexaweb.

Web 2.0 application tends to interact with the end user and the end user had a greater role in the web 2.0 applications as he/she is not only the user of the application but also a participant. This may be through tagging the content, contributing to wiki, by podcasting or blogging. The user also provides feedback on the applications in addition to their social contribution to the applications.

One of the key components of Web 2.0 are web services, and how these applications expose their functionality and can be combined with other applications to provide a rich set of new applications using mashups. Computer languages are required to perform these tasks, and it is very important to update the applications frequently so the many users get up to date information. Some of the applications of Web 2.0 are Flickr, Delicious (formerly del.icio.us), YouTube, Facebook and MySpace

Performance
The speedup of a program as a result of parallelization is given by Amdahl's law. Amdahl's Law states that potential program speedup is defined by the fraction of code (P) that can be parallelized: 1/(1-P)

If the code cannot be broken up to run over multiple processors, P = 0 and the speedup = 1 (no speedup). If it is possible to break up the code to be perfectly parallel then P = 1 and the speedup is infinite (in theory, although other factors such as scalability and complexity limit this possibility). Thus, there is an upper bound on the usefulness of adding more parallel execution units. Gustafson's law is a law closely related to Amdahl's law but doesn’t make as many assumptions and tries to model these factors in the representation of performance. The equation can be modelled by S(P) = P − α * (P − 1) where P is the number of processors, S is the speedup, and α the non-parallelizable part of the process.

Parallel Processing
Parallel processing is the use of multiple CPUs to execute different sections of a program together. Remote sensing and surveying equipment have been providing vast amounts of spatial information, and how to manage, process or dispose of this data have become major issues in the field of Geographic Information Science (GIS).

To solve these problems there has been much research into the area of parallel processing of GIS information. This involves the utilization of a single computer with multiple processors or multiple computers that are connected over a network working on the same task. There are many different types of distributed computing, two of the most common are clustering and grid processing.

Why Use Parallel Processing

 * The primary reasons for using parallel computing:
 * Save time - wall clock time
 * Solve larger problems
 * Provide concurrency (do multiple things at the same time)


 * Other reasons might include:
 * Taking advantage of non-local resources - using available computing resources on a wide area network, or even the Internet when local computing resources are scarce.
 * Cost savings - using multiple "cheap" computing resources instead of paying for time on a supercomputer.
 * Overcoming memory constraints - single computers have very finite memory resources. For large problems, using the memories of multiple computers may overcome this obstacle.


 * Limits to serial computing - both physical and practical reasons pose significant constraints to simply building ever faster serial computers:
 * Transmission speeds - the speed of a serial computer is directly dependent upon how fast data can move through hardware. Absolute limits are the speed of light (30 cm/nanosecond) and the transmission limit of copper wire (9 cm/nanosecond). Increasing speeds necessitate increasing proximity of processing elements.
 * Limits to miniaturization - processor technology is allowing an increasing number of transistors to be placed on a chip. However, even with molecular or atomic-level components, a limit will be reached on how small components can be.
 * Economic limitations - it is increasingly expensive to make a single processor faster. Using a larger number of moderately fast commodity processors to achieve the same (or better) performance is less expensive.
 * The future: during the past 10 years, the trends indicated by ever faster networks, distributed systems, and multi-processor computer architectures (even at the desktop level) clearly show that parallelism is the future of computing.

Grid Computing
Some consider this to be the “the third information technology wave” after the Internet and Web, and will be the backbone of the next generation of services and applications that are going to further the research and development of GIS and related areas.

Grid computing allows for the sharing of processing power, enabling the attainment of high performances in computing, management and services. Grid computing, (unlike the conventional supercomputer that does parallel computing by linking multiple processors over a system bus) uses a network of computers to execute a program. The problem of using multiple computers lies in the difficulty of dividing up the tasks among the computers, without having to reference portions of the code being executed on other CPUs.

Local search
Local Search is a recent approach to internet searching that incorporates geographical information into search queries so that the links that you return are more relevant to where you are. It developed out of an increasing awareness that many search engine users are using it to look for a business or service in the local area. Local search has stimulated the development of web mapping, which is used either as a tool to use in geographically restricting your search (see Bing Maps ) or as an additional resource to be returned along with search result listings (see Google Maps). It has also led to an increase in the number of small businesses advertising on the web.

Distributed GIS – Acronym Index
AIS	Automatic Identification System

CAT	Catalogue Service

CID	Complete Intervisibility Database

DEG	Display Element Generator

GSDI (Geo)Spatial data infrastructure|Spatial Data Infrastructure

NGDF	National Geospatial Data Framework

NSDI	National and International Spatial Data Infastructures

OGDI	Open Geographic/Geospatial Datastore Interface

OGSA	Open Grid Services Architecture

SDI Spatial Data Infrastructure

SRS Spatial Referencing System

WMC	Web Map Context