  Van der Waals heterostructures display a rich variety of unique electronic
properties. To identify novel transport mechanisms, nonlocal measurements have
been widely used, wherein a voltage is measured at contacts placed far away
from the expected classical flow of charge carriers. This approach was employed
in search of dissipationless spin and valley transport, topological
charge-neutral currents, hydrodynamic flows and helical edge modes. Monolayer,
bilayer, and few-layer graphene, transition-metal dichalcogenides, and moire
superlattices were found to display pronounced nonlocal effects. However, the
origin of these effects is hotly debated. Graphene, in particular, exhibits
giant nonlocality at charge neutrality, a prominent behavior that attracted
competing explanations. Utilizing superconducting quantum interference device
on a tip (SQUID-on-tip) for nanoscale thermal and scanning gate imaging, we
demonstrate that the commonly-occurring charge accumulation at graphene edges
leads to giant nonlocality, producing narrow conductive channels that support
long-range currents. Unexpectedly, while the edge conductance has little impact
on the current flow in zero magnetic field, it leads to field-induced
decoupling between edge and bulk transport at moderate fields. The resulting
giant nonlocality both at charge neutrality and away from it produces exotic
flow patterns in which charges can flow against the global electric field. We
have visualized surprisingly intricate patterns of nonlocal currents, which are
sensitive to edge disorder. The observed one-dimensional edge transport, being
generic and nontopological, is expected to support nonlocal transport in many
electronic systems, offering insight into numerous controversies in the
literature and linking them to long-range guided electronic states at system
edges.
