Table 1.

Summary of STDM main challenges and their causes

Issue	Challenges	Causes	Tasks	Applications
Spatio-temporal Relation-ships	Complexity	Discrete representation of continuous spatiotemporal data	S-Rao et al. (2012); Shekhar et al. (2015), CA-Du et al. (2016); Huang et al. (2008), PA-Cheng et al. (2020), OD-Rettig et al. (2015), PM-Liang et al. (2019); Zhang et al. (2019); Fusco et al. (2016), V-Eldawy et al. (2016)	PS-Zhang et al. (2017), TM-Wang et al. (2016), EA-Guo (2017), EP-Lee et al. (2016), SA-Tsou (2015), IoT-Wang et al. (2016)
		Co-located objects influence each other
	Implicit-ness	Implicit relationships between spatiotemporal objects	CA-Senaratne et al. (2014); Kang et al. (2020), PA-Sagl et al. (2012); Aydin et al. (2016), OD-Radhakrishna et al. (2016), PM-Chung et al. (2017)	PS-Wu et al. (2015), TM-El Esawey (2017), EA-Guo (2017), EP-Welch et al. (2011), SA-Sagl et al. (2012), IoT-Sagl et al. (2012)
	Non-independ-ent and Non-identical distrib-ution	Auto-correlation due to dependency relationships in space and time	S-Shekhar et al. (2015), CA-Khan et al. (2017); Guijo-Rubio et al. (2020), PA-Shirowzhan et al. (2020), OD-Khan et al. (2017), PM-He et al. (2019); Jiang and Shekhar (2017), V-Li et al. (2017)	PS-Quick et al. (2017), TM-Cheng et al. (2012), EA-Fawcett et al. (2014), EP-Meentemeyer et al. (2011), SA-Kim et al. (2016), IoT-Gao (2015)
		Non-identical distribution across space and time
Inter-disciplin-ary and Combined Data Mining	Various interrelated domains	Heterogeneous data requiring multiple STDM techniques	CA-Carrasco-Escobar et al. (2017); Shao et al. (2019), PA-Yates et al. (2015), OD-Harris et al. (2014), PM-Jiang and Shekhar (2017), V-Pattelli et al. (2016) VA-Malik et al. (2014),	PS-Song et al. (2017), TM-Cheng et al. (2012); Yates et al. (2015), EA-Fawcett et al. (2014), EP-Hanke et al. (2016), SA-Cao et al. (2015), IoT-Xue et al. (2016)
	Environ-mental factors
	Opportunity
Region Discretization	Scale effect	Scale dependency	CA-Damm et al. (2020), PA-Nelson and Brewer (2017); Zeng et al. (2020), OD-Gutiérrez-Gómez et al. (2020), PM-Yuan et al. (2020); Sadri et al. (2018), V-Nelson and Brewer (2017), VA-Malik et al. (2014); Zeng et al. (2020)	PS-Quick et al. (2017), TM-Ling et al. (2020), EA-Liu et al. (2014), EP-Lee et al. (2016), SA-Cao et al. (2015), IoT-Kotevska et al. (2017)
	Zoning effect	Zone dependency
Data Characteristics	Specificity	Spatiotemporal data tend to be unique to a particular space-time region.	CA-Rashidi et al. (2015), PM-Zhao et al. (2015), V-Phillips and Lee (2012); Van Pelt et al. (2012), VA-Malik et al. (2014)	PS-Malik et al. (2014), EA-Rashidi et al. (2015) SA-Zhao et al. (2015)
		Learned model is specific to a particular spatiotemporal region.
	Vagueness	Similarities rooted from different criteria	S-Shekhar et al. (2015), CA-Senaratne et al. (2014); Kang et al. (2020), PA-Aydin et al. (2016), OD-Radhakrishna et al. (2016), PM-Chung et al. (2017)	PS-Albertetti (2015); Wu et al. (2015), TM-El Esawey (2017), EA-Guo (2017), EP-Welch et al. (2011), SA-Sagl et al. (2012), IoT-Sagl et al. (2012)
	Dynamic-ity	Continuous change through space and time.	CA-Huang et al. (2008), PA-Liu et al. (2014), OD-Shahid et al. (2015); Ferreira et al. (2020), PM-Hens et al. (2019); Ehrlén and Morris (2015); Rumi et al. (2018), V-Cheng et al. (2020)	PS-Kotevska et al. (2017), TM-Cheng et al. (2012); El Esawey (2017), EA-Liu et al. (2014), EP-Meentemeyer et al. (2011), SA-Cao et al. (2015), IoT-Kotevska et al. (2017)
	Social	Correlation with the socio-economic characteristics	CA-Steiger et al. (2016), OD-Chae et al. (2012), PM-Rumi et al. (2018); Zhao et al. (2015); Bogomolov et al. (2014); Zhou et al. (2017), V-Hochman and Schwartz (2012); Tsou (2015) VA-Cao et al. (2015)	PS-Bogomolov et al. (2014), SA-Rumi et al. (2018); Zhao et al. (2015), IoT-Wang et al. (2020); Kaur et al. (2018); Chae et al. (2012)
	Network-ed	Influence between objects and trajectories.
		Exponential number of relationships.
	Heterog-eneous and Non-stationary	Wide variation of data distributions over space and time.	S-Miller and Han (2009); Yu and Liu (2017), CA-Carrasco-Escobar et al. (2017), PA-Ren et al. (2018); Yates et al. (2015), OD-Harris et al. (2014), PM-Jiang and Shekhar (2017); Rahaman et al. (2018), V-Pattelli et al. (2016) VA-Malik et al. (2014)	PS-Kadar et al. (2019); Song et al. (2017), TM-Cheng et al. (2012); Yates et al. (2015), EA-Fawcett et al. (2014), EP Hanke et al. (2016), SA-Cao et al. (2015), IoT-Yang et al. (2019b); Xue et al. (2016)
		Different learning models for varying spatiotemporal regions.
	Limited Access and Privacy	Privacy issues	S-Giannotti and Pedreschi (2008), CA-Acs and Castelluccia (2014), PA-De Montjoye et al. (2013), PM-Huang et al. (2020)	PS-Ratcliffe (2010), TM-Kaltenbrunner et al. (2010), IoT-De Montjoye et al. (2013)
	Poor Quality	Uncertainties, Partial knowledge, Conjectures	CA-Albertetti (2015), PM-Diehl et al. (2015) V-Islam et al. (2018) VA-Malik et al. (2014)	PS-Malik et al. (2014); Murray et al. (2011), EA-Diehl et al. (2015), SA-Steiger et al. (2016), IoT-Wang et al. (2018b)
	Big data	Volume, variety and velocity	CA-Du et al. (2016); Shao et al. (2016), PA-Cheng et al. (2020),PM-Fusco et al. (2016), OD-Rettig et al. (2015), V-Eldawy et al. (2016)	PS-Zhang et al. (2017), TM-Wang et al. (2016), EA-Guo (2017), EP-Lee et al. (2016), SA-Tsou (2015), IoT-Wang et al. (2016)
Open Issues	Data Representations	Limited representations of spatiotemporal data	Santos et al. (2016); Dunkel et al. (2019); Gao et al. (2020); Yu et al. (2020); Golany et al. (2020)
	Advanced Modelling	Depend on high-density locations while ignoring the temporally related attributes.	Roth et al. (2013); Nguyen et al. (2017); Almanie et al. (2015); Fusco et al. (2016); Du et al. (2016); De Brouwer et al. (2019); Chen et al. (2018); Sen et al. (2019); Kim et al. (2018)
	Visualisation	Developing techniques for spatial visualisation, while less consideration is given to spatiotemporal	Ye et al. (2012); Kastner and Samet (2020); Sakaue and Sato (2020); Rizwan et al. (2020); Salcedo-Gonzalez et al. (2020); Sha et al. (2020)
	Comprehen-sive Approaches	Focusing on certain problems and do not introduce comprehensive spatiotemporal solutions	Ndehedehe et al. (2016)
	Fairness, Accountability, Transparency, and Ethics (FATE)	Amplifying genders, denying people services, and racial biases .	Dudík et al. (2020); Olteanu et al. (2020); Buolamwini and Gebru (2018); Raghavan et al. (2020); Blodgett et al. (2020); Guo et al. (2019); Bird et al. (2020)