An important problem in distributed and networked sensing is registration of coordinate systems or synchronisation of clocks across the network. The main problem discussed in this talk is as follows. We have a network of sensors each with its own local coordinate system. We are given noisy measurements of the transformations connecting the coordinate systems of certain pairs of sensor in the network. The goal is to find local algorithms which will, in a optimal statistical sense, align the coordinate systems across the network. The talk will show how this problem can be formulated as a gauge invariant statistical estimation problem, how it is related to the homology of graphs, and how statistical optimal local estimators can be constructed in a number of cases.