Background: Social support is a crucial factor influencing the sustainability of physical activity (PA). This proof-of-concept study presents the development of a Social Physical Activity Index for Area (SPAIFA) an indicator reflecting opportunities for individuals to actively participate as part of a group within which opportunities for social interaction can be developed. Methods: Six government councils in the state of New South Wales, Australia, were selected encompassing 174 suburbs. Using 2 search engines' map tools, we identified PA venues for each suburb (eg, park, studios, etc). To enumerate activities per suburb, we used (1) venue websites, (2) New South Wales Office of Sport website, (3) national websites of grassroots PA for nonorganized activity (eg, parkrun, meetup, etc), and (4) social media. The database was linked to the suburb demographic profile, the area disadvantage score, walkability and open space scores, and the proportion of insufficiently active residents. Spatial analysis techniques were used to identify SPAIFA clusters. Results: SPAIFA councils' average was 9.9 activities per 10,000 people (ranging from 6.6/10,000 to 16.2/10,000). SPAIFA-Old (ie, activities specific to older adults) varied significantly (ranging from 11.7/10,000 to 0.8/10,000 seniors). Disadvantaged areas and a high proportion of insufficiently active residents were associated with being classified as low SPAIFA (P <.01). Three clusters of low SPAIFA were identified, and 17 high-risk areas where low SPAIFA was compounded by poor environmental support. Conclusions: SPAIFA can be used by councils and policymakers as an indicator for monitoring and intervening in areas where natural and/or urban design is not conducive for PA. [ABSTRACT FROM AUTHOR]