  Propelled by versatile data capture, communication, and computing
technologies, physical sensing has revolutionized the avenue for spontaneously
capturing and interpreting real-world phenomenon. Despite its virtues, various
limitations (e.g., high application specificity, partial autonomy, and sparse
coverage) hinder physical sensing's effectiveness in critical scenarios such as
disaster response. Meanwhile, social sensing is contriving as a pervasive
sensing paradigm that leverages the observations from human participants
equipped with portable devices and ubiquitous Internet connectivity (i.e.,
through social media or crowdsensing apps) to perceive the environment. While
social sensing possesses a plethora of benefits, it also inherently suffers
from a few drawbacks (e.g., inconsistent reliability, uncertain data
provenance, and limited sensing availability). Motivated by the complementary
virtues of both physical and social sensing, social-physical sensing (SPS) is
protruding as an emerging sensing paradigm that tightly integrates social and
physical sensors at an unprecedented scale. The vision of SPS centers on
mitigating the individual weaknesses of physical and social sensing while
exploiting their collective strengths in reconstructing the "state of the
world", both physically and socially. While a good amount of interesting SPS
applications has been explored, several important unsolved challenges and open
research questions prevail in the way of developing dependable SPS systems,
which require careful study to address. In this paper, we provide a
comprehensive survey of SPS, with an emphasis on its definition and key
enablers, state-of-the-art applications, potential research challenges, and
road-map for future work. This paper intends to bridge the knowledge gap in
current literature by thoroughly examining the various aspects of SPS crucial
for building potent SPS systems.
