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participants (vendors) to collaborativeiy research, develop and 
demonstrate new Standards-based Commercial technologies 
that enable your web browser to seamlessly access, view and 
exploit the vast, diverse and widely distributed geospatial data 
holdings on the Web. The first round of the WMT was started in 
May of 1999 and completed in September 1999. The Web 
Mapping Testbed Phase 2 (WMT 2) expands the range of 
interoperable web mapping services to meet a broader 
cross-section of community needs. In addition to creating new 
specifications, WMT 2 will result in more federal data coming 
on-line using WMT protocols. The WMT rapidly produces 
interface specifications that enable interoperability and 
innovation. 
3. WHAT IS GML? 
The Geography Markup Language (GML) is an XML 
encoding for the transport and storage of geographic 
information, including both the geometry and properties of 
geographic features (OpenGIS Consortium, 2000). GML is 
based on a common model of geography (OGC Abstract 
Specification), which has been developed and agreed to by the 
vast majority of all GIS vendors in the world. 
GML version 1.0 is developed by OGC as a Recommendation 
that was passed in May 2000, and OGC announces the release 
of Geography Markup Language version 2.0 (GML) in April 4, 
2001, a significant milestone in the development of 
interoperable architectures for the use of spatial information 
between commercial applications. The progress of GML 2.0 is 
an example of the growing momentum for the acceptance and 
use of OGC specifications around the world. GML represents 
one of the most visible steps taken by the geospatial community 
towards the vision of widespread spatial interoperability. GML 
was originally implemented and tested through a series of 
demonstrations that formed part of the OGC's Web Mapping 
Testbed (WMT) conducted in the summer of 1999. These tests 
involved GML mapping clients interacting with GML data 
servers and service providers. Further exploration and 
development of GML is now taking place within OGC's Web 
Mapping Testbed Phase II and Geospatial Fusion Services 
Testbed Phase I. 
The Features of GML includes: 
• GML encodes Feature Geometry and Properties 
• GML encodes Spatial Reference Systems 
• GML can transport geographic information and store 
geographic information as well. 
• GML can readily Integrate with Non-Spatial Data 
• GML implements data transform between XML-to-XML. 
• GML can transport behavior 
4. WEB MAPPING WITH GML 
Geographic data is concerned with a representation of the 
world in spatial terms that is independent of any particular 
visualization of that data. When we talk about geographic data, 
we are trying to capture information about the properties and 
geometry of the objects that populate the world about us. How 
we symbolize these on a map, the colors or line weights we 
choose to use is something quite different. Just as XML now 
helps to clearly separate content from presentation for web 
pages, so GML will do the same in the world of geography and 
mapping (Ron Lake, 2000). 
GML is concerned with the representation of geographic data 
content. As well, we shall see we can also use GML to make 
maps. This might be accomplished by developing a rendering 
tool to interpret GML data. However, this would conflict with the 
GML approach to standardization, and to the separation of 
content and presentation. 
To make a map with GML data, we must style the GML 
geographical content into a suitable graphical presentation. This 
involves the interpretation of the GML content using graphical 
symbols, and often some sort of transformation of the geometry 
of the GML data into the geometry of the visual presentation. 
We refer to this interpretation process as map styling (Ron Lake, 
2001). Many of the same tools and technologies, such as XSLT 
(XML Transformation Language), can be used to perform this 
styling operation. Potential graphical display formats include 
W3C Scalable Vector Graphics (SVG), Vector Markup 
Language (VML), and the Web 3D Consortium's X3D. 
XSLT is well suited to XML-to-XML transformations. XSLT is 
extensible. XSLT supports the concept of an extension function. 
An extension function allows an XSLT engine to perform 
operations that are beyond the capabilities of the XSLT 
language such as geometric or coordinate transformations. In 
the majority of cases we may use XSLT as a tool to style the 
GML data into an XML graphical format such as SVG VML or 
X3D. 
The process of transforming the graphical presentation into a 
viewable image we shall refer to as graphical rendering. At the 
present time there are a variety of graphical renders available 
for each of the different XML graphical formats, some native to 
the browser (e.g. Internet Explorer 5.0's built in VML processor),