  Propelled by the omnipresence of versatile data capture, communication, and
computing technologies, physical sensing has revolutionized the avenue for
decisively interpreting the real world. However, various limitations hinder
physical sensing's effectiveness in critical scenarios such as disaster
response and urban anomaly detection. Meanwhile, social sensing is contriving
as a pervasive sensing paradigm leveraging observations from human participants
equipped with portable devices and ubiquitous Internet connectivity to perceive
the environment. Despite its virtues, social sensing also inherently suffers
from a few drawbacks (e.g., inconsistent reliability and uncertain data
provenance). Motivated by the complementary strengths of the two sensing modes,
social-physical sensing (SPS) is protruding as an emerging sensing paradigm
that explores the collective intelligence of humans and machines to reconstruct
the "state of the world", both physically and socially. While a good number of
interesting SPS applications have been studied, several critical unsolved
challenges still exist in SPS. In this paper, we provide a comprehensive survey
of SPS, emphasizing its definition, key enablers, state-of-the-art
applications, potential research challenges, and roadmap for future work. This
paper intends to bridge the knowledge gap of existing sensing-focused survey
papers by thoroughly examining the various aspects of SPS crucial for building
potent SPS systems.
