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What is the Urban Heat Island?

Cities are hot — much hotter than their surroundings due to a phenomenon known as the Urban Heat Island effect. Roads, buildings, and sidewalks tend to be much hotter than forests, grasslands, and other vegetation. The concentration of people and cars, too, generates a lot of heat within cities. Climate change is also making the Urban Heat Island effect worse, by increasing the frequency and likelihood of heat waves that can elevate temperatures over long time periods and put sensitive populations – the elderly, the young, and those with other vulnerabilities to heat stress – at risk. 

In addition to age and health, a variety of factors can affect how people experience the Urban Heat Island effect. For example, where you work and live can make a difference – some neighborhoods might be less dense and have more shaded areas and green space that can provide some relief to urban heat. Some people have access to public transportation, air conditioning, or private vehicles that could protect them from heat exposure. Other weather variables, such as wind speed, visibility, and humidity, also affect how individuals experience urban heat. But how exactly all of these factors come together to affect an individual’s thermal comfort, however, is a question limited by the availability of high-resolution, individual-scale data.

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Our Solution

To address these knowledge gaps, we have partnered with researchers at the BUDS Lab at the National University of Singapore to adapt Cozie – an iOS application to gauge human thermal comfort using smartwatches and smartphones.


What is Cozie?

Here we introduce Cozie to our Urban Heat study! Cozie is an iOS App for human comfort data collection. It was originally designed and developed by Dr. Federico Tartarini, Dr. Clayton Miller, and Dr. Stefano Schiavon. It is a light and easy-to-use survey app that allows people to provide their thermal comfortness in real-time! Here at Data-Driven EnviroLab, we customized Cozie for our Urban Heat Study.

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Instruction of Cozie


1. How to install Cozie on your device?

Currently, Cozie at DDL is still under beta testing. If you are participating in the North Carolina Urban Heat Effect Mapping Campaign, you should have received an invite link to Cozie already. Or if you are interested in using Cozie at DDL for Urban Heat Study, please contact us. If you may be interested in tailoring Cozie for your own study, please contact Dr. Tartarini.

  • Please make sure you are using an iPhone with at least iOS 9. If you would like to use your Apple Watch, please make sure it is at least gen 3 or newer. We are still working on the development to support more versions of Apple and Android products. 
  • Please install TestFlight on your phone. You can find it in the App Store. 
  • Open your invitation email or tap on the public invite link on your phone
  • Tap View in TestFlight or Start Testing; or tap Install or Update for the app you want to test.

2. First Time Using Cozie.

  • The first time you open Cozie on your device, the app will ask you Notification preference, please allow Cozie to send you Notifications.
  • As a new user, please create an account by clicking “Sign Up”. Your email and password will be securely stored in our cloud. We are using Firebase SDK for authentication. If you are coming back for Cozie, please click Login. Please make sure the password is at least 8 characters long and contains a special character and a number.
  • After you created an account, the app will ask you for your location. Please select “Allow While Using App” as the location information is critical to this study. 
  • If you are also using Apple Watch, please ensure that the Cozie application was successfully installed on your Apple Watch. To install Cozie on your Apple Watch, open the “Watch” app on your iPhone. Tap the My Watch tab. Then, scroll to Cozie. Cozie should appear in the Available Apps section. Tap install. 
  • This may take 10 minutes or longer depending on your connection.
  • (Please skip this step if you are only using iPhone only) Open the Cozie app on your Apple Watch as if you were about to complete a survey. Then open the iOS app on your phone, go to the Settings tab and click on Send participant ID to watch. Make sure the phone and the watch are close to each other, and that the app on the watch is open when you click on that button. You may need to click twice. If the pairing was successful the watch should vibrate and you should hear a notification sound.


  • ** Special Note: The original User Interface was designed for iPhones with a screen size of at least 4.7 inches. If you are using a 4-inch screen size iPhone like iPhone SE (1st generation), you will encounter a small screen issue: the keyboard covers the “Sign Up” button on the sign-up page and the task cards on the home page are cropped on the left and right sides.

    Now in the latest version of Cozie (1.08), we allow users to hide the keyboard on the sign-up page by tapping the white space on that page or clicking “return” on the keyboard (See pictures below). Please note that this is a quick fix for signing up using a small-screen iPhone, the UI of the task cards is still cropped (See pictures below). We will keep fixing these UI issues and finalizing the details in the future. But these issues will not prevent small-screen iPhone users to use Cozie for the survey. Thank you for your patience and understanding!



3. On-boarding!

  • After you set up Cozie on your iPhone or Watch, firstly, please open the Eligibility card and answer the questions. Make sure you are eligible for this study (18 years older or older)
  • Then, please review the Consent card. In the end, you will be asked to sign the form if you agree with this consent. You can also find the full consent form from our GitHub
  • After that, please finish the Onboarding card. Note that, you only need to finish this card once!
  • The Survey card is where all the survey questions are. Please complete this survey at least three times during the campaign. Please answer the survey at different places if possible, as we want to capture the data under different circumstances. If you are using an Apple Watch, you should be able to finish these survey questions on your watch as well.



Please find the full consent form here:


To help us better understand your experience with Cozie, you are welcome to fill in this survey! Click Here. Your time and feedback will be much appreciated! We will keep making improvements to Cozie and provide the best experience to users 🙂

Contact Information

This app was originally developed and designed by Federico Tartarini, Clayton Miller, and Stefano Schiavon. Please kindly find the source page here: Xuewei Wang and Joyce Mei of the Data-Driven EnviroLab customized the app to meet the NC Urban Heat Island Temperature Mapping Campaign. If you have questions or concerns about your rights as a research subject you may contact the UNC-CH Institutional Review Board at 919-966-3113 or Name and Contact of Principal Investigator: Angel Hsu – Name and Contact of Study Administrator: Xuewei Wang –