Citizens as Voluntary Sensors: Spatial Data Infrastructure in the World of Web 2.0

Much progress has been made in the past two decades, and increasingly since the popularizing of the Internet and the advent of the Web, in exploiting new technologies in support of the dissemination of geographic information. Data warehouses, spatial data libraries, and geoportals have proliferated, and today’s users of geographic information have a wealth of potential sources that can be searched for suitable data sets. Standards have been established, issues of syntactic interoperability have been largely addressed, and rich descriptions are available in metadata to allow the suitability of a given data set to be assessed. Table digitizers used to be an essential asset for any spatial data center in the days when most sources of geographic information were in the form of paper maps, and skill in digitizing was a major part of any introduction to geographic information systems (GIS). Today, however, users rely heavily on digital sources, and virtually all digitizing is heads-up on-screen.