  We construct the phase space of 3-dimensional asymptotically flat spacetimes
that forms the bulk metric representation of the BMS group consisting of both
supertranslations and superrotations. The asymptotic symmetry group is a unique
copy of the BMS group at both null infinities and spatial infinity. The BMS
phase space obeys a notion of holographic causality and can be parametrized by
boundary null fields. This automatically leads to the antipodal identification
of bulk fields between past and future null infinity in the absence of a global
conical defect.
