Mapping Underground — Privacy Policy

Effective date: 3 September 2026

Mapping Underground is a crowd-sourced project that maps underground spaces using smartphone sensors. This policy describes what the mobile app records, what happens to that data, and the choices you have.

What the app records

The app records data only while a recording session you started is running. A session captures, exactly as the sensors report it:

• Motion sensors: accelerometer, gyroscope, magnetometer, and hardware step counts
• Barometric pressure
• GPS positions — received above ground, including where you start and end a session
• Identifiers of nearby cellular network towers
• Technical metadata: timestamps, device model and operating system version, sensor capabilities of the device, battery level, session settings, and app lifecycle events during the session

Recordings are uploaded verbatim, without on-device editing or filtering. Completed recordings upload after the session ends — by default only over Wi-Fi, so the upload may happen some time later. Outside of a session the app records nothing; the GPS status shown before you start a recording never leaves your device.

What the app does not collect

• No account, name, email address, or phone number — the app has no sign-up
• No hardware device identifiers: uploads are tagged with a random pseudonym generated by the app, which you can reset at any time from the app's settings. Note that recordings can still be related to each other through their content — for example repeated GPS positions or cellular tower identifiers — which processing uses to align journeys
• No advertising, analytics, or cross-app tracking of any kind in the app (this website uses analytics — see "Website analytics" below)
• No health data — only raw motion sensor readings and step counts

How recordings are used

Recordings are processed to estimate the trajectory of each journey and to fuse many journeys into shared maps of underground spaces. Raw recordings are not sold or shared with third parties; they are stored in access-controlled cloud storage, transferred over encrypted connections (HTTPS), and accessible to the project's operators. Maps built from everyone's recordings may be published — the places you record can appear in them, so do not record in places you would not want on a map.

Deletion

You can remove a recording's local copy from your device at any time. To have an uploaded recording permanently deleted, email us at the address below — deletion removes the raw data and marks anything derived from it for recomputation without your contribution. In-app deletion of uploaded recordings is planned.

Website analytics

This website (not the app) uses Google Analytics to understand how many people visit and which pages they view. Google Analytics sets cookies and receives technical information about your visit — pages viewed, approximate location derived from your IP address, and browser and device type — which is processed by Google on our behalf under Google's privacy policy. We use it only for aggregate visit statistics; we do not use it for advertising. You can block analytics with a browser content blocker or Google's opt-out add-on. Sensor recordings uploaded by the app are never shared with Google Analytics, and the app itself contains no analytics.

Children

The app is not directed at children under 13 and does not knowingly collect data from them.

Changes

If this policy changes, the new version will be posted at this address with an updated effective date.

Contact

Questions, feedback, or deletion help: mappingunderground@andreithuler.com