Original Research ARTICLE
Early Indicators of Human Activity During COVID-19 Period Using Digital Trace Data of Population Activities
- 1Department of Civil and Environmental Engineering, Texas A&M University, College Station, TX, United States
- 2Department of Computer Science and Engineering, Texas A&M University, College Station, TX, United States
- 3Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States
- 4Community Team, Mapbox, Washington, DC, United States
The spread of pandemics such as COVID-19 is strongly linked to human activities. The objective of this article is to specify and examine early indicators of disease spread risk in cities during the initial stages of outbreak based on patterns of human activities obtained from digital trace data. In this study, the Venables distance (
The objective of this study is to reveal and evaluate early indicators of human activity during COVID-19 period in cities at the initial stages of the outbreak using measures of human activities derived from digital trace data. As an arguably unprecedented global pandemic, the coronavirus disease 2019 (COVID-19) has infected millions of people worldwide with a mortality rate of 6.6% and a high infection rate (Keni et al., 2020; World Health Organization, 2020). Since the spread of COVID-19 is highly dependent on human activities, incidence of infection could be contained by restricting human activities and mobility (Gollwitzer et al., 2020). Many countries and authorities have implemented various nonpharmaceutical interventions (e.g., shelter-in-place orders, regional lockdowns, and travel restrictions), which were undertaken to slow the spread of disease by disrupting transmission chains through restricting human mobility and activities. Such social distancing and activity reduction interventions have proven to be critical in slowing down the spread of pandemics both in previous epidemics (Caley et al., 2008) and during COVID-19 (Anderson et al., 2020; Tian et al., 2020; Li, et al., 2020b; Ramchandani, et al., 2020).
While reduction in human activities is considered an effective measure for containing epidemics and pandemics, there are limited reliable, proven, real-time leading indicators related to human activities that could provide early insights about the risk of disease spread in a region to inform proactive policy making. One reason for this limitation has been the absence of quantitative measures and data that could be examined to proactively evaluate human activities. With advancements in location intelligence data technologies, however, information derived from cellular devices offers a large depository of digital trace data related to human activities increasingly adapted and analyzed to promote understanding of and to quantify human activity and mobility in pandemic analysis, as well as in other applications (Balcan et al., 2009; Asgari et al., 2013; Barbosa et al., 2018). For example, in the context of COVID-19, the radius of gyration, which captures the mobility of individuals using human movement trajectories, was adopted to analyze the COVID-19 spread in Japan (Yabe et al., 2020). Daily step-counts (gathered from smartphones) were used to estimate and predict decreased movement of individuals within the United States during COVID-19 (Gollwitzer et al., 2020). Two of the most important aspects of human activities during an epidemic are agglomeration of activities and intensity of activities.
Although previous research reveals insights regarding human activities in the context of COVID-19, the relationship between human activities and disease-spreading risk has not been fully explored, and leading indicators of human activities to proactively assess the risk of disease spread during the early stages of pandemics are lacking. The majority of research studies (Chang et al., 2020; Cintia et al., 2020; Gao et al., 2020; Li et al., 2020a) focus on quantifying and analyzing the changes in human activities as a consequence of the outbreak of the virus and in response to protective policies (such as shelter-in-place policies). The time-lag relationship between these human activity metrics and the spread of virus, which can be generally described by the basic reproduction number (
In this study, the empirical data related to human activities during COVID-19 was used to reveal the leading relationship between the human activity and the basic reproduction number. We adopted the Venables distance (
The rest of this article is organized into three sections. The first section discusses the description of the two datasets (Mapbox data and total confirmed cases number data), as well as the analysis methods. The second section describes the results of time-lag correlation analysis between the two metrics and the basic reproduction number. The last section presents the results and the implications of the findings for future work.
In this section, we describe the two datasets—Mapbox data and total confirmed cases number data—and the procedures for human activity categorization. Also covered in this section are definitions and equations related to the Venables distance (
Data Source and Preprocessing
We utilized digital trace telemetry data obtained from Mapbox from January 1 to March 30, 2020. The dataset contains a metric of telemetry-based human activity,
FIGURE 1. 193 selected counties whose cumulative confirmed cases were greater than 100 as of March 31, 2020.
To reveal the time-lag relationship between metrics and spread of the virus, the total number of confirmed cases was used. We obtained the data from the COVID-19 Data Repository by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University (2020). The data in this repository were gathered and aggregated from various sources, such as the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). We extracted the total number of confirmed cases
The nature of an activity might put its participants at a higher risk level for contracting the virus. For example, activities in public common areas, such as grocery stores or gyms, would lead to greater risk of disease spread compared to the activities in residential areas, such as working from home or walking a dog in the community. The fine granularity of the spatial resolution enables classification of each tile into one of the four categories: (1) social tiles, (2) traffic tiles, (3) work tiles, and (4) other tiles. Categorization is based on the following characteristics: (1) social tiles are the location of at least one point of interest location; the location information of point of interest is extracted from SafeGraph data (including restaurant, gas station, and commercial complex) (SafeGraph, 2020); (2) traffic tiles are extracted by mapping the traffic network with all tiles including roads; (3) work tiles are identified based on lack of activity during the late evening hours; and (4) other tiles are located in residential areas. We assigned these four tags to each tile from social, traffic, work to other. Once a tile is assigned with a tag, it is excluded for further categorization. We categorized tiles in this way to examine the importance of human activity in each category and its relationship with the reproduction number. The analysis in this research examines human activities for social, work, and traffic tiles separately. All the residential tiles are excluded from the analysis because the human activities in these tiles have less influence on the contact level among people. Example tile maps related to each category are shown in Figure 2 for Harris County, Texas.
FIGURE 2. Maps of four different tile categories (social, traffic, work, and other) in Harris County, Texas.
To quantify the agglomeration of human activities, we used the Venables distance (
Activity Density (
Basic Reproduction Number Estimation
The basic reproduction number (
Time Lagged Cross-Correlation Analysis
In the next step, we examined the correlation between the two human activity indicators and the basic reproduction number across all counties. Since these variables are a time series, we used time-lagged cross-correlation analysis to assess the synchrony of time series data sets. The cross-correlation coefficient was calculated using Eq. 7:
This section presents the results related to the calculation of the two human activity metrics and their time-lagged correlation with the basic reproduction number across 193 counties during the initial stage of the COVID-19 outbreak in the United States.
Evaluation of Human Activity for Each Category Among Counties
In this study, the Venables distance (
FIGURE 3. The percentage change of
FIGURE 4. The percentage change of
The increasing trend of Venables distance (
Histograms of average percentage change of
FIGURE 5. Histogram plots of average percentage change of
Time-Lagged Correlation Analysis
The spread of the coronavirus is closely related to the human activity patterns. In the previous section, we showed that the average distance between human activities (
FIGURE 6. The time-lagged correlation analysis between Venables distance (
FIGURE 7. The time-lagged correlation analysis result between activity density (
Figure 7 shows the time offset result between activity density (
Heterogeneity for Different County Features
In the next step, we examined the variation of findings across counties with different population sizes, number of confirmed cases, and date of first confirmed cases. The goal is to examine the extent to which the correlation between the two metrics of human activities and the reproduction number is sensitive to these county features. The 193 counties were divided into three uniform categories according to population size and confirmed cases (on March 18, 2020) labeled high, medium, and low. Similarly, the first case dates were labeled as early, mid-range, and late for each one-third of counties. Then, the changes in
FIGURE 8. Change in Venables distances (
This study shows the utility of two human activity metrics [the Venables distance (
There exist other studies that examined human mobility in the context of COVID-19. Wang et al. (2020) examined the similar time-lag effect of human mobility on the COVID-19 infections in the 80 cities most affected in China from Jan 17 to Feb 29. The results showed that the time lag is about 10 days. The index of intracity traffic volume (provided by Baidu) was used to represent the human mobility. Such highly aggregated data, however, may lose some critical spatial information about human activities. Xiong et al. (2020) analyzed mobile device data at each United States county for the COVID-19 period. The origin-destination travel demand and aggregate mobility inflow were used to represent the human activities, and the results showed the dynamics in a positive relationship between human mobility and COVID-19 transmission. Compared with the mentioned similar metrics describing human activities, the two indicators in this article (
This study has some limitations which need to be improved in future studies. First, the tile activity categorization—social, work, and traffic—is not precise. One tile could be labeled as both social and work. In this study and due to data availability limitations, however, we classified tiles into only one of the three categories. Second, the CDC confirmed-cases data had limitations due to testing availability. In this study, we did not adjust the confirmed case data based on the extent of testing in different counties. A lack of testing in some areas resulted in the underestimation of the total cases.
Data Availability Statement
The data analyzed in this study is subject to the following licenses/restrictions: the data that support the findings of this study are available from Mapbox, but restrictions apply to the availability of these data, which were used under license for the current study and so are not publicly available. Requests to access these datasets should be directed to Mikel Maron, firstname.lastname@example.org.
Research design and conceptualization were carried out by XG, CF, and AM; data collection, processing, analysis, and visualization were performed by XG, CF, YY, SL, and QL; writing was done by XG and AM; reviewing and revising were made by all authors.
This work was supported by several grants including the United States National Science Foundation RAPID project #2026814, Urban Resilience to Health Emergencies: “Revealing Latent Epidemic Spread Risks from Population Activity Fluctuations and Collective Sense-making,” and Microsoft AI for Health COVID-19 Grant for cloud computing resources.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The authors would also like to acknowledge that Mapbox provided digital trace telemetry data of human activity and that SafeGraph provided POI data. The authors would like to thank Kieran Gupta, Sofia Heisler, and Ruggero Tacchi from Mapbox for providing technical support.
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Keywords: COVID-19, early indicators, population activities, time lag relationship, Venables distance, activity density
Citation: Gao X, Fan C, Yang Y, Lee S, Li Q, Maron M and Mostafavi A (2021) Early Indicators of Human Activity During COVID-19 Period Using Digital Trace Data of Population Activities. Front. Built Environ. 6:607961. doi: 10.3389/fbuil.2020.607961
Received: 18 September 2020; Accepted: 29 December 2020;
Published: 04 February 2021.
Edited by:Samiul Hasan, University of Central Florida, United States
Reviewed by:Yuan Liao, Chalmers University of Technology, Sweden
Takahiro Yabe, Purdue University, United States
Copyright © 2021 Gao, Fan, Yang, Lee, Li, Maron and Mostafavi. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Xinyu Gao, email@example.com
†These authors have contributed equally to this work