The base of large scale mapping of urban heat islands (UHI) is a large amount of spatial information which can be highly expensive to collect. Our Department has also experimented with using wireless sensor networks; however, it is more efficient and cheaper to collect data provided by volunteers. Young volunteers (primary and secondary school students) are relatively easy to motivate, and direct contact can be built up between project managers and volunteers through teachers. Volunteered geographic information (VGI), created by young volunteers, was collected with the help of Web 2.0 technology. It was complemented by traditional scientific geographic information collected by wireless sensors developed for air temperature measurement. Geospatial analysis of recorded VGI for urban heat islands was used for a better understanding of spatial relationship between urban land cover and UHI, and of the rapid change of UHI due to changing meteorological conditions. Large scale UHI maps were generated using VGI to uncover hidden structures in UHI. These maps were compared to the medium scale UHI maps, which were created by impervious surface maps derived from spectral mixture analysis of a Landsat TM image.