  We present a decentralised class of algorithms called Tree-Proof-of-Position
(T-PoP). T-PoP algorithms rely on the web of interconnected devices in a smart
city to establish how likely it is that an agent is in the position they claim
to be. T-PoP operates under adversarial assumptions, by which some agents are
incentivised to be dishonest. We present a theoretical formulation for T-PoP
and its security properties, and we validate this model through a large number
of Monte-Carlo simulations. We specifically focus on two instances of T-PoP and
analyse their security and reliability properties under a range of adversarial
conditions. Use-cases and applications are discussed towards the end of this
paper.
