Web GIS is currently the fastest growing area of the GIS industry, and Web is now seen as a standard for most applications.

This section concentrates on explaining some of the key concepts of Web GIS, and therefore contains some level of technical detail. For a less technical view of Web GIS review the Benefits or Customer Needs of Web GIS.

This section is designed to aid an understanding of how Web GIS will complement and fit with your existing or proposed GIS and IT infrastructure. This section does not purport to cover all technical aspects of Web GIS, and those described here are at a relatively high, often conceptual level.

The power of Web GIS lies in its versatility, practicality, flexibility and simplicity. These are described below in the following terms:-

Enterprise Web GIS refers to the access and use of GIS data and functions through a Web Browser, whether it be via an Intranet, Internet or Extranet.

This access is possible through either wire-line or wireless (mobile) devices. We concentrate mainly on the wire-line access to GIS in this section. More information on access to GIS data through mobile technology is described in Mobile GIS.

ESBI Computing have our own powerful Enterprise Web GIS application called GeoXplorer™, and reference is made to it where relevant.

Users

Users of Web GIS are many and varied and can be classified by:

• Role or technical expertise - Data technician, business manager or casual user
• Industry - Utility or Manufacturing company
• Customer needs - Marketing, Planner etc

Independent of the type of Industry or the nature of the particular Customer needs (both of which are described elsewhere), GIS users can be summarised into the following roles and user needs:

Data

Data is the core component of any system not least an Enterprise Web GIS. A GIS has three main types of data:

Spatial data

Spatial data is data that can be represented by a known location on a map in a specific co-ordinate system. Spatial data (graphic data or geometry) is normally represented visually as points, lines or areas (polygons or regions). It can also be images which have been geo-referenced so that they have a know location. Spatial data can therefore be stored as:

• Physical geometry in a proprietary or 'open' GIS data format,
• Geo-referenced images, or
• In an RDBMS in spatial database tables.

Non-spatial data

Non-spatial data is non-graphic textual data such as exists in most enterprise RDBMS. It can be linked to spatial data through an address or geo-code, which allows this non-spatial data to be viewed and analysed through its location. It is widely quoted that up to 85% of data in most enterprise databases has a spatial dimension i.e. it can be represented in a GIS, therefore most data can be converted into spatial data.

External data

Spatial and non-spatial data can be internal to an enterprise or can be external 'third party' data, which can be used by the enterprise to leverage the power of GIS. ESBI Computing can supply 'third party' spatial and non-spatial data, and a variety of data services to enable the establishment of an Enterprise Web GIS.

Ease of data access and management

The Enterprise Web GIS can simply and seamlessly access data from all over an enterprise and present it to the user without the user needing to understand the location of the data on the network or the data's structure. Here lies one of the most significant benefits of Web GIS. Enterprise Web GIS greatly simplifies access to all enterprise data, and through the power of location allows disparate data sets to be inter-related and relationships and patterns analysed.

The Enterprise Web GIS accesses the original base of spatial or non-spatial data, performs functions on the data and returns a processed version of the data to the user via the web browser. This browser data is normally:

• A simple image eg. .gif or .jpeg
• Simple vector data

Applications

While data is critical to any Enterprise Web GIS, the Web GIS Applications themselves are the workhorses of the solutions. The type of information and functionality provided via the applications varies depending on :-

• The type of network access eg. Intranet or Internet
• The type of users and their requirements
• The type of end user devices eg. mobile may have display limitations

Web GIS Applications come in many forms, which differ mainly by :-

• Range of functionality
• Type of client browser interface eg. thick, medium or thin
• Data connectivity and flexibility
• Ease of set-up and customisation
• Design or architecture
• Underlying technology eg. Java or Microsoft
• Scalability and adaptability

We will now expand on these first three points

Range of functionality

Web GIS solutions can include a wide range of complex functionality or just very basic functionality. What is required depends on the type of users and the type of network i.e. is it Intranet or Internet. Web GIS can be customised relatively easily, so the same base product can be customised up or down. New user/application specific functionality can be added as modules.

Web GIS functionality can also be relatively easily integrated into other solutions eg. Internet web sites. Typical functionality includes :-

• Visualisation - basic and thematic mapping - of spatial and non-spatial
• Query - database and spatial data
• Editing - add, modify and delete spatial & non-spatial data
• Output

Type of client browser interface

Complex functionality can be provided using more sophisticated browser capabilities. Browser clients can be thin, medium or thick.

• Thick clients usually rely on plug-ins (which must be downloaded) that allows processing in the browser, necessitating less on the application server. They may also allow data to be downloaded to the client in encrypted formats.
• Medium browser clients require downloadable (on runtime) applets to allow the user extra interactivity with the application eg. multiple clicks (which is essential for some functionality eg. editing).
• Thin clients require the server application to do the processing. Another type of client, which is discussed elsewhere, is Mobile GIS.

Data connectivity and flexibility

Web GIS permits access to a wide variety of spatial and non-spatial data in maps, relational and non-relational databases. Web GIS applications allow easy connection to GIS and enterprise databases, and these can be queried and edited depending on user privileges. It is important that the solution can access spatial and non-spatial data from anywhere in the enterprise in its original format, to avoid data duplication.

ESBI Computing have developed a Web GIS Application called GeoXplorer™ which provides:

• A broad range of GIS functionality, which can be easily customised or expanded with additional modules, and
• Easy data set up and database connectivity to allow painless integration of spatial and non-spatial enterprise and third party data.

Technology components

There are three main components of an Enterprise Web GIS:

The key components of an Enterprise Web GIS solution are probably the servers, as these provide the richness of data and functionality. The network influences performance and therefore may limit the complexity of data and functionality.

There is a fourth additional Location element which is not strictly an integral part of Enterprise Web GIS, although it may use data feeds from Mobile GIS devices in the field to :-

• Show/track their location
• Update information real-time on location

These three basic components of Enterprise Web GIS technology (plus Location) are shown in the diagram below, and described in more detail later.

The main Components of an Enterprise Web GIS solution

The Network

There are three main types of Web GIS solutions (plus Mobile) and these are mainly differentiated by their network access i.e.

Performance is affected by the type of network, and therefore the type and complexity of devices, data and functionality. GeoXplorer™ has been successfully deployed in Intranet and Internet networks.

The Servers - GIS Content Providers

This is arguably the most significant technical component of an Enterprise Web GIS solution, which serves data (information) and applications (functionality) to the user.

There are two main types of servers:

• GIS Servers
• Gateway Servers (which are required to support mobile applications, and are described under Information Processing Services and Gateway Servers).

GIS Servers are :

• Web servers
• Application servers
• Map servers
• Data servers

The functions of these servers are described below, but several or all functions can be :-

• Combined onto one server
• Divided between many servers (as 'distributed' or 'scalable' solutions), eg.
  • The Web & Application server can be one server
  • The Web, Application & Map server can be one
  • All four functions can be provided by one server (not recommended), or
  • Each function can run on several servers

The recommended approach is to have separate servers if budget and technical context permits. The number of servers and their power i.e. number and power of processors (CPU) and memory, affect the performance of a web GIS solution, and its cost. Load balancing can be applied to any of the servers to improve performance.

Web servers

Web servers communicate with the client devices via the network. These receive requests from the client, invoke the application server, and serve back responses to the client. The web server requests services from the application server.

Application servers

These manage server transactions and securities. An application server manages requests from the Web server and passes them to the Map server.

Map servers

Map servers are the workhorses of Web GIS solutions, and performs many functions similar to traditional GIS. The map server processes client requests and generates results. The Map server executes spatial queries and analysis and generates and delivers maps to the client via the application and web servers. It executes the relevant functionality and accesses the relevant data from the data servers.

Data servers

The data server serves spatial and non-spatial data from relational or non-relational database structures. These servers can be one or many:

• Dedicated GIS data servers - spatial and non-spatial data
• Enterprise data servers, which exist outside the GIS infrastructure

GeoXplorer™ is developed using Microsoft Active Server Pages (ASP) as its application server and the powerful MapInfo^® MapXtreme^® NT as its map server. It is deployed using Microsoft Internet Information Server (IIS) as the Web server. Data servers can be anywhere in your enterprise, once accessible via networking.

The Client

The client is where users interact with spatial data via a Web browser using the functionality provided in the Web GIS, and subsequently view and output the results. Web clients fall into three main categories of devices:

• Desktop PC's
• Laptop PC's
• Mobile devices

Web GIS browser clients, which run on these devices, can be:

• Thick
• Medium, or
• Thin

Go to types of client browser interfaces for more information.

GeoXplorer™, which is a medium client, uses a small Java applet, which is downloaded on application start-up. This allows GeoXplorer™ to have more powerful interactive functionality via the browser.

ESBI Computing have a mobile GIS application called GeoMobile, which can be used to provide powerful location based data capture functionality in the field.

The Location (the Mobile element)

The location component of Web GIS technology is delivered through mobile field-based clients with Position Determining Devices (PDE), which can be either :-

• Global Positioning Systems (GPS)
• Triangulated mobile phone cell id's

These components are vital for Web GIS applications which rely on real-time location information on vehicles and staff, or for the provision of Location Based Services (LBS). The mobile devices update the Web GIS with information on their location, or may be used to update GIS databases with changes to spatial and non-spatial data real-time, which are vital for work scheduling and assets management and planning systems.

For more information on this technology go to Position Determining Devices under Mobile GIS.

ESBI Computing's mobile application GeoMobile works with GPS to provide powerful location based data capture functionality in the field.