ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001 
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WEB MAPPING WITH GEOGRAPHY MARKUP LANGUAGE 
Xingling WANG Chongjun YANG Donglin LIU 
Institute of Remote Sensing Applications, Chinese Academy of Sciences 
P.O.Box 9718, Beijing, China 100101 
Tel: 86-10-64889212 Fax: 86-10-64889206 Email: wxl@digitalearth.net.cn 
KEYWORD: XML, Web Mapping, GML 
ABSTRACT: 
XML (extensible Markup Language) provides a powerful new way for data description and data exchange, and it is becoming widely used 
on the World Wide Web. Over 100 XML derived languages emerging in last year. In March of 2000, OpenGIS have proposed a format to 
represent geographical information with XML, which is called GML (Geography Markup Language). GML is a powerful new way for 
geographic information sharing, interoperability and Web Mapping. This paper represents a GML-based Web Mapping application that 
public spatial data via the web. The new web will be a semantic web. With GML, spatial data will be integrated within the semantic web 
totally. 
1. INTRODUCTION 
XML is the “extensible Markup Language” that was 
developed by the World Wide Web Consortium. XML is an idea 
data format for storing structured and semi-structured text 
intended for dissemination and ultimate publication on a variety 
of media (Robin Cover, W3C 1998). Over 100 XML derived 
languages emerging in last year. There are two subtle but 
keenly important differences between HTML and XML. 
SoftwareAG (makers of Tamino, an XML based database) 
explains the distinction this way: The motto of HTML is: "I know 
how it looks," whereas the motto of XML is: "I know what it 
means, and you tell me how it should look.“ Said another way, 
HTML is about making pretty presentations while XML is a 
semi-structured document that holds "content". Various 
techniques based on the XML are under an intensive 
development by the World Wide Web Consortium (W3C). 
In the world of GIS we are still a ways off from extensive 
adoption of XML, as researchers and vendors explore and 
define how XML will be used (Adena Schutzberg, 2000). ESRI 
has chose XML to store metadata in Arclnfo 8. The data is in a 
raw format, and depending on your needs can be displayed in 
different ways. Gl, Geographic Information, community's 
interest in this new technology is exemplified by the various 
initiatives to adopt XML syntax as a encoding language for 
spatial data. Examples include the ISO TC211's work on 
developing rules for expressing UML-modeled datasets in an 
XML vocabulary and the Open GIS Consortium's (OGC) 
recently introduced Geography Markup Language (GML). The 
W3C is also developing an XML-based Web vector graphics 
specification, called Scalable Vector Graphics (SVG). Since the 
number of XML-encoded spatial datasets available on the Web 
is evidently going to increase, a question must be raised about 
how these datasets might be used. Many client applications will 
not be able to process spatial information in it's original form. 
The W3C's recent Recommendation, extensible Stylesheet 
Language Transformations (XSLT), is a power tool to 
pre-process spatial XML-based datasets into a more 
easy-to-use form. 
2. WHAT’S WEB MAPPING? 
Web Mapping is the set of products, standards and 
technologies that enable access to location information, usually 
portrayed as maps, via the Web(OGC, 2000). 
Unfortunately, today, most Web Mapping applications are 
inseparably tied to a specific server implementation. In other 
words, the client is hard coded to interact with a particular 
vendor's proprietary map server implementation. User must run 
different client applications in order to access the data and 
functionality provided by different server implementations. In 
this situation, there is very little interoperability or reuse of client 
and server implementations. Because data are often accessible 
only through a given server, there is also very limited ability for a 
user to transparently access data of interest from outside a fixed 
client/server. 
The Open GIS Consortium's Web Mapping Testbed (WMT) is 
a process that brings together sponsors (customers) and