Walk, ride, or descend underground — Signal Mapper logs where your cellular connection is strong, weak, or dead, and draws it on a map.
Enter the invite id, then the name you were given.
The app is private — you log under an invite id. First time in, it asks for two things:
1. Paste your invite id (an invite link fills it in for you).
2. Type the name you were given, tap Start.
That device stays logged in. A new device just asks for your name again — tap change on the top line any time.
Hit Start Mapping. Each reading runs a tidy four-step cycle — kept in order so GPS and the cellular radio don't fight: Locate → settle → measure speed → save.
It repeats on a timer until you tap Stop. Lose signal in a tunnel? Readings are saved on the phone and uploaded automatically when you're back online.
While a run is active, the context buttons mark a stretch:
Prefer talking? Use your phone's voice-memo app — its timestamps line up with the run later.
The Map tab plots every reading, colored by download speed:
Toggle the Dead-zone heatmap overlay — the hottest red areas are your weakest spots.
See its speed, ping, accuracy and time, then exclude a bad fix (hides it, no delete) or annotate it. Filter by run, or reveal hidden points with the excluded toggle.
Every Start = one run. The Runs tab lists them with point counts, average speed and dead-zone counts. Per run you can:
Export a GeoJSON from the Survey tab (everything) or per-run in the Runs tab.
Drop it into kepler.gl (color by speed for an instant heatmap), geojson.io, or Mapbox. Surface readings are points; subway/transit runs also draw a path line.