Geographical location is now widely used on the Web as a means to link two or more existing sources of information to create a new service, providing information that would otherwise have been unavailable. These combined services are commonly known as mashups, from a term used in the recording industry to refer to music created by combining previously independent tracks. Together they form what is often termed the GeoWeb, a spider’s web of services held together through the use of geographical location, whether expressed as latitude/longitude, place name, street address, or any other convenient system of georeferencing.

As an example, houses listed for sale on Craigslist (www.craigslist.com) are first analyzed by a mashup service to obtain their street addresses, which are then converted to latitude/longitude using a Web-based geocoding service (see Figure). The mashup service, www.housingmaps.com, combines these coordinates with a mapping service (Google Maps, maps.google.com) to provide detailed and useful maps of where houses are listed for sale, along with other information about the house—something that neither Craigslist nor Google Maps is capable of providing on its own.

A map of houses currently listed for sale in the $150,000-300,000 price range by Craigslist for part of Los Angeles. This www.housingmaps.com mashup combines Craigslist data with Google Maps. SOURCE: www.housingmaps.com.