  Since the industrial revolution, accelerated urban growth has overflown
administrative divisions, merged cities into large built extensions, and
blurred the boundaries between urban and rural land-uses. These traits, present
in most of contemporary metropolis, complicate the definition of cities, a
crucial issue considering that objective and comparable metrics are the basic
inputs needed for the planning and design of sustainable urban environments. In
this context, city definitions that respond to administrative or political
criteria usually overlook human dynamics, a key factor that could help to make
cities comparable across the urban fabric of diverse social, cultural and
economic realities. Using a technique based on the spectral analysis of complex
networks, we rank places in 11 of the major Chilean urban regions from a
high-resolution human mobility dataset: Official origin-destination (OD)
surveys. We propose a method for further distinguishing urban and rural
land-uses within these regions, by means of a network centrality measure from
which we construct a spectre of geographic places. This spectre, constructed
from the ranking of locations as measured by their approximate number of
embedded human flows, allows us to probe several urban boundaries. From the
analysis of the urban scaling exponent of trips in relation to the population
across these city delineations, we identify two clearly distinct scaling
regimes occurring in urban and rural areas. The comparison of our results with
land cover derived from remote sensing suggests that, for the case of trips,
the scaling exponent in urban areas is close to linear. We conclude with
estimations for well-formed cities in the Chilean urban system, which according
to our analysis could emerge from clusters composed by places that capture at
least ~138 trips (over the expectation) of the underlying mobility network.
