This study proposes a middleware based on a geographical information system (GIS) and related information as part of an initiative toward open data platforms, which has been undertaken by countries such as the USA, UK, Australia, and India through websites with names like ′data.gov′. Other governments, including Australia, with a national map of 2D map information have not yet provided GIS-based open data and open application programming interfaces (APIs). On the other hand, the Korean government has actively opened up GIS-based information called VWorld and open APIs. However, the building industry has not yet exploited this information, and it seems to lack accessibility. Therefore, authors aim to support fast and expanding open data and propose a middleware that uses VWorld as a target platform for searching, processing, and generating GIS-based open data toward realizing building information modelling (BIM) exchangeable information. A Web 2.0 based middleware should be different from a Web 1.0 counterpart so that open data from suppliers are guided and delivered to data consumers in customized data formats. Authors expect that this study will serve as a general guiding approach for harvesting GIS-based open data as soon as other governments provide open data in the near future. Therefore, it should lead to dramatic improvements in acquiring environmental information relevant to building design, thus enabling better decision-making during design.