This paper proposes an optimal allocation problem with ramified transport
technology in a spatial economy. Ramified transportation is used to model the transport
economy of scale in group transportation observed widely in both nature and efficiently
designed transport systems of branching structures. The ramified allocation problem aims at
finding an optimal allocation plan as well as an associated optimal allocation path to
minimize overall cost of transporting commodity from factories to households. This problem
differentiates itself from existing ramified transportation literature in that the
distribution of production among factories is not fixed but endogenously determined as
observed in many allocation practices. It's shown that due to the transport economy of
scale in ramified transportation, each optimal allocation plan corresponds equivalently to
an optimal assignment map from households to factories. This optimal assignment map
provides a natural partition of both households and allocation paths. We develop methods of
marginal transportation analysis and projectional analysis to study properties of optimal
assignment maps. These properties are then related to the search for an optimal assignment
map in the context of state matrix.