claim: San Francisco Bay Area is home to approximately 10 million people.
evidence: Volunteered geographic information -LRB- VGI -RRB- is the harnessing of tools to create , assemble , and disseminate geographic data provided voluntarily by individuals -LRB- Goodchild , 2007 -RRB- .. Goodchild. Michael Frank Goodchild. VGI is a special case of the larger Web phenomenon known as user-generated content .. user-generated content. user-generated content. Some examples of this phenomenon are WikiMapia , OpenStreetMap , and Google Map Maker .. WikiMapia. WikiMapia. OpenStreetMap. OpenStreetMap. Google Map Maker. Google Map Maker. VGI can also be seen as an extension of critical and participatory approaches to geographic information systems .. geographic information systems. geographic information systems. VGI attracted concerns about data quality , and specifically about its credibility and the possibility of vandalism .. data quality. data quality. credibility. credibility. vandalism. vandalism. These sites provide general base map information and allow users to create their own content by marking locations where various events occurred or certain features exist , but are n't already shown on the base map .. One of the most important elements of VGI in contrast to standard UGC is the geographic element , and its relationship with collaborative mapping .. collaborative mapping. collaborative mapping. The information volunteered by the individual is linked to a specific geographic region .. While this is often taken to relate to elements of traditional cartography , VGI offers the possibility of including subjective , emotional , or other non-cartographic information .. Geo-referenced data produced within services such as Trip Advisor , Flickr , Twitter and Panoramio can be considered as VGI .. Trip Advisor. Trip Advisor. Flickr. Flickr. Twitter. Twitter. Panoramio. Panoramio