Recent advances in mobile computing technology have made it increasingly common for collocated users to perform collaborative photography over a large physical space in various group activity scenarios such as field trips, site surveys, and group tours. Unlike traditional collocated interactions in a shared physical space, we find that mobility and group dynamics make awareness of group activities over a large physical space very challenging. In this work, we design LetsPic, a group photoware that supports group awareness for in-situ collaborative photography over the large physical space. We have iteratively built the app and performed user studies in site survey and group tour scenarios (n = 31, n = 24). Our results confirmed that LetsPic effectively promotes group awareness, facilitates group coordination, and encourages collaboration in both scenarios. We discuss practical design implications based on our findings.