OpenGeoSpatial Consortium (OGC) specification on Web ... fications; e. g., MapWindow GIS, a client-side application, ... may even consume data sources from each other, build- .... the maps on these devices are displayed by a mobile web.
Web Feature Service (WFS) and Web Map Service (WMS)
to the requesting client in the form of GML. The visibility and use of this data is realized only after it is rendered in the form of maps. However, it is clear that WFS provides the raw material (data) for the finished product (the rendered map). The tremendous utility of web feature service is that a requestor of information can choose to use the raw data in any number of ways. For instance, the client may store the data or display the data. Future Directions As Web Feature Services is a protocol, it is under constant review and changes. This is especially so because it is a protocol that deals with web services in the upcoming area of geospatial services. The latest specification as well as the ones before it can be found at the Open GeoSpatial Consortium (OGC) website (http://www.openspatial.org). Cross References Geography Markup Language (GML) Web Feature Service (WFS) and Web Map Service
(WMS) Web Services, Geospatial
Recommended Reading 1. OpenGeoSpatial Consortium (OGC) specification on Web Feature Service (http://www.opengeospatial.org/standards/wfs): According to the OGC website, (http://www.opengeospatial.org), OGC is a non-profit, international, voluntary consensus standards organization that is leading the development of standards for geospatial and location based services. It provides technical documents that detail agreed-upon interfaces or encodings which when implemented by software developers will ensure that the resulting components work together coherently 2. Web Mapping Illustrated by Tyler Mitchell (O’Reilly Series, 2005). This book explains how to find, collect, understand, use, and share mapping data, both over the traditional Web and using OGC-standard services like WFS and WMS 3. Beginning MapServer: Open Source GIS Development by Bill Kropla (Apress Publications, 2005). This book shows the use of OGC-standard services in MapServer, one of the popular development platforms for integrating mapping technology into Internet applications 4. http://www.en.wikipedia.org: This collaborative web-based, free content encyclopedia project is a good resource to see information on WFS brought together. It provides additional links for further investigation
Web Feature Service (WFS) and Web Map Service (WMS) C HRISTOPHER D. M ICHAELIS, DANIEL P. A MES Department of Geosciences, Geospatial Software Lab, Idaho State University, Pocatello, ID, USA
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Synonyms Internet mapping service; MapServer; ArcIMS; ArcExplorer; Web processing service; WFS; WMS
Definition Open Geospatial Consortium (OGC) standards for the exchange of geospatial data form a consistent foundation for the development of geographic information systems (GIS) software. The Open Geospatial Consortium (http:// www.opengeospatial.org/) is a leading body in standards development in GIS, consisting of members across diverse scientific backgrounds [1]. The most widely adopted and popular of these is the Web Map Service (WMS), a specification which outlines communication mechanisms allowing disjoint software products to request and provide preassembled map imagery (“compiled” map images, which may contain both vector and raster data) to a requesting client. A similar service, Web Feature Service (WFS), allows clients to request vector data which is returned in a pure form (preserving the vector nature of the dataset). Another service which is raising in popularity though not yet a formal specification is the Web Processing Service (WPS) proposal. This illustrates a mechanism by which a client may request geoprocessing to be performed on a server, in a similar fashion to that available in ESRITM ArcIMS software which also allows clients to perform GIS processing and analysis via the Internet. While ArcIMS protocols to this end are not published, OGC specifications which outline communications protocols aim to be open. Software (whether client-side or server-side) implementing these key specifications gains the advantage of being interoperable with other geospatial software. An excellent example of this is MapServer, produced by the University of Minnesota, which acts as a server for both WMS and WFS communications mechanisms [3]. WMS and WFS servers may be high-end datacenter servers or even a personal workstation computer. Data exposed by MapServer through these specifications may be consumed by any client software implementation which supports the specifications; e. g., MapWindow GIS, a client-side application, or the Refractions Research web-based client tool (http:// mapserver.refractions.net/phpwms/phpwms-cvs/). Servers may even consume data sources from each other, building maps upon resources spread throughout the internet. MapServer again serves as an example: in addition to providing WMS and WFS data, it can also consume WFS and WMS data from other servers to render maps for an end user.
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Web Feature Service (WFS) and Web Map Service (WMS)
Historical Background Web-based geographic information system (GIS) tools are becoming very common for many basic mapping and data visualization tasks (e. g., GoogleTM Maps, MapQuestTM , and ArcIMS). However, desktop or client-side GIS tools are likely to continue to be heavily used by government, academic, and commercial users requiring a high degree of custom data management, modeling, and analysis functionality. The primary standards issuing entity for the GIS community, the Open Geospatial Consortium (OGC), has released many specifications which are not necessarily web-specific, yet the most widely adopted of its standards are specifically for web based GIS tools. Because of this, it is likely that most GIS users and tool developers (specifically those developing tools for the desktop GIS environment) are unaware of OGC standards and specifications and their potential implications. Specific OGC standards such as Web Map Service (WMS) and Web Feature Service (WFS) have significant potential for normalizing, and hence improving, the manner in which data is shared across the Internet. Most day to day users may be concerned with how to use data provided by these services in their client-side GIS applications, but many may also be interested in using this data in their own server-based tools for providing maps. The stated mission of the OGC is “to lead the global development, promotion and harmonization of open standards and architectures that enable the integration of geospatial data and services into user applications [2].” This is accomplished through the authoring of specifications which are created by “structured committee programs and a consensus process” by which participants in a wide range of scientific disciplines may contribute to the specifications. A specific goal of the OGC is to address the problem of data sharing – a problem that includes both interoperability and communication – and ultimately arrive at “a world in which everyone benefits from the use of geospatial information and supporting technology”. OGC has attempted to address some of the fundamental problems of data sharing by specifying a common format for wide-scale understandability in distribution, for facilitating geoprocessing, and for interoperability between disjoint software products. It is of note that the OGC produces standards with respect to data transfer and communications; but not in metadata areas. The FGDC and ISO standards are the main issuing entities for metadata standards. Scientific Fundamentals A tightly defined XML (eXtensible Markup Language) schema may easily keep servers and clients interoperat-
ing successfully despite being written by varied authors for various platforms. Most OGC specifications make use of XML schemas in this manner. The first such example is Web Map Service (WMS), with which a client may request a map image from a server. This is then returned in a standard imaging format (e. g., JPEG). The request is authored using XML such that the server will understand exactly how to parse and understand the request. The image is returned without any geographic location information (e. g., a “world file”), since this service is primarily used for end-user interfaces and not mosaic operations or similar operations requiring geographic location information. Frequently, server implementations will return exactly the spatial extents requested, making the returning of this particular metadata less important. In WMS, the key communications are performed using XML documents which list the available data on a server (the GetCapabilities request), which provide details on a given dataset (the DescribeLayer request), or which request a map image as described above (the GetMap request). The Web Feature Service (WFS) uses XML more extensively. Similarly to WMS, operations to list data on a server (GetCapabilities) and to describe a dataset (DescribeLayer) are used. Rather than returning an image from a GetMap request, WFS will provide vector data, without first assembling it into a standard image format (which tends to lose data quality and precision). The word “feature” in this service is referring to a vector object such as a point, line, or polygon, and the word carries some history of its own. A client may request vector data from a server in a manner similar to that used in WMS (a tightly defined XML schema is used). The server responds with the requested vector information encoded in Geographic Markup Language, a separate standard which defines a common and open format for communicating geographic and geometric data. Because WFS uses GML, which is also based on XML, this causes a greater quantity of XML text to be transferred. Some advantages to this are that XML is designed to be easily parsed by machine yet also easily readable by humans – thus making debugging easier and helping the user to understand what is taking place. A major disadvantage, however, is the overhead associated with transmitting XML tags and all data in an essentially text-based format. Binary data transmission could cut the total number of bytes to be transmitted nearly in half – a staggering amount of overhead. While this overhead is huge, it is often disregarded due to high internet connection speeds and due to the ease of working with XML data. WFS is not as heavily adopted as WMS, potentially due to the greater overhead and computational power required to use it, but is nonetheless used widely across the internet.
Web Mapping and Web Cartography
An example of when WFS may be appropriate rather than WMS may be if geospatial operations will need to be performed on the data (e. g., for a calculation or for a model), rather than simply using the data for end user visualization. A related service, Web Processing Service, has been proposed but not yet formally accepted as an Open Geospatial Consortium specification. This proposal outlines a mechanism by which a server may perform geoprocessing operations as requested by a client, using XML communication mechanisms very similar to those observed with WFS and WMS. Though the proposal has not been adopted widely, some investigation into the feasibility of WPS has been done and shows great promise. Using the system outlined by the proposal, a client may encode input data and transmit it to a server, requesting a given operation to be performed. Processing may take place on the server, with output data being returned back to the client upon completion. GML is again used for vector data, and binary formats or base-64 encoded data are often used for raster data.
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Web GIS Internet GIS
Web Graphics Standard Scalable Vector Graphics (SVG)
Web Map Server University of Minnesota (UMN) Map Server
Web Map Service deegree Free Software OGC’s Open Standards for Geospatial Interoperability Web Feature Service (WFS)
Key Applications The best known software package implementing WFS and WMS is MapServer. This package acts as both a client and server for WFS and WMS data, meaning that it can serve data in these formats as well as consume this data from other servers. Other applications that can consume WFS and WMS data include OpenEV, ArcExplorer, MapWindow GIS and uDig, among others. Future Directions WFS and WMS have already shown great potential for providing data using a common communications mechanism across the internet. Server tools and end-user applications will undoubtedly continue to adopt these standards, allowing for further data sharing. WPS, though it hasn’t been widely used or adopted, shows great potential as applications developers begin to adopt it and make greater use of the proposed specification. Cross References Web Services
Recommended Reading 1. Open Geospatial Consortium, Inc. Filter Encoding Implementation Specification, OGC Website: http://www.opengeospatial. org/ (2001) 2. Open Geospatial Consortium, Inc. Vision and Mission, OGC Website: http://www.opengeospatial.org/about/?page=vision (2006) 3. University of Minnesota. MapServer, MapServer Website: http:// mapserver.gis.umn.edu/ (2006)
Web Mapping and Web Cartography A NDREAS N EUMANN Institute of Cartography, ETH Zurich, Zurich, Switzerland Synonyms Electronic atlases; Maps on internet; Mobile maps; SVG; Web technologies; CGI; Web server; Web application server; Web mapping server; WMS Definition Web mapping is the process of designing, implementing, generating and delivering maps on the World Wide Web. While web mapping primarily deals with technological issues, web cartography additionally studies theoretic aspects: the use of web maps, the evaluation and optimization of techniques and workflows, the usability of web maps, social aspects, and more. Web GIS or Internet GIS is related to web mapping but with an emphasis on analysis, processing of project specific geodata as well as exploratory aspects. Often the terms web GIS and web mapping are used synonymously, even if they don’t mean the same. In fact the boundary between web maps and web GIS is blurry. Web maps are often a presentation media in web GIS and web maps are increasingly gaining analytical capabilities. A special case of web maps are mobile maps, displayed on mobile computing devices, such as mobile phones, smart phones, PDAs, GPS and other devices. If the maps on these devices are displayed by a mobile web browser or web user agent, they can be regarded as mobile
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