The World Wide Web presents many new, exciting prospects for geographic information systems, but also numerous technical, practical and organizational challenges. Users no longer require specialized and expensive hardware, software and data, and they can access a GIS readily from almost anywhere, using off-the-shelf browser software.An online GIS removes the need to collate all the necessary elements in a single database. Instead it has the potential to seamlessly combine datasets that are stored on many different servers and maintained by many different organizations. However, to realize this potential it is crucial to develop appropriate standards and protocols. Such problems belong to the realm of "spatial metadata" which forms the basis of this book.The book covers the principles, techniques and standards for online GIS, including online spatial information and data warehousing. It examines the idea of metadata and outlines why it is important today, especially in the context of online information. It explains the underlying methodologies, including relevant standards, and the tools and skills needed to manage metadata. Finally, the subject is placed in the context of global GIS: putting data online; creating metadata; creating virtual data warehouses; geographical agents, and spatial data mining.