A topic map is a formalism to represent knowledge about the structure of an information resource and to organize it in topics. These topics have occurrences and associations that represent and define relationships between them. Information about the topics can be inferred by examining the associations and occurrences linked to the topic. A collection of topics and associations is called a topic map .
Topic maps can be seen as a description of what is about a certain domain, by formally describing topics, and by linking the relevant parts of the information set to the appropriate topics .
The tool used to develop topic map is tm4l (Topic Map for e-learning) 
(i) TM4L Editor and Viewer
(iv) Tmproc etc.
TM4L (Topic Maps for e-Learning) is an authoring environment that supports the creation, maintenance, and use of ontology-aware courseware based on the ISO standard – Topic Maps. As an alternative to conventional authoring systems TM4L is aimed at facilitating the integration of already existing learning resources on the web. The TM4L Editor can be used also as a general Topic map development tool. It includes software developed by the TM4J Project.
OMNIGATOR: The Omnigator is a technology showcase and teaching aid designed to demonstrate the power of Topic Maps. It is also used extensively as a topic map debugger and prototyping tool. Its most unique feature is that it lets you load and navigate any conforming topic map, whether its format be XTM, HyTM, LTM – or even RDF.
4) D.V.Janardhan Rao, T.V.Prabhakar, Jayanta Chatterjee and M.D.Singh, A Topic Map driven Portal for Agriculture Information by IIT Kanpur. URL:http://opaals.iitk.ac.in/deal/other/topic_map.pdf
10) Piedad Garrido, Jesús Tramullas (2004), Topic Maps: An Alternative Or A Complement To Concept Maps, Universidad de Zaragoza, España. URL:http://cmc.ihmc.us/papers/cmc2004-226.pdf
14) Steve Pepper. The TAO of Topic Maps-finding the way in the age of infoglut. URL:http://www.ontopia.net/topicmaps/materials/tao.html
17) http://www.ontopia.net/omnigator/models/index.jsp (Last Accessed- June 2008)
18) http://www.topicmap.com/topicmap/tools.html (Last Accessed- June 2008)