Your phone can see dozens of WiFi networks at once — each one a little radio beacon broadcasting
its name and signal strength from a fixed location. The number of networks, their signal strengths,
and their names tell you a lot about where you are: residential suburb, dense apartment building,
office tower, shopping centre, or open countryside.
Google and Apple have mapped the location of every WiFi network on Earth using their users' phones.
Every time a phone does a location lookup, it scans nearby WiFi networks and reports their
signal strengths to a central server — along with your GPS coordinates. Apple has over 100 million
access points in its database. In 2010, Google's Street View cars were caught collecting not just
WiFi network names but actual packet data from open networks. Your network is in the database whether
you opted in or not.
Browsers can read your connection speed and RTT — but not the list of nearby networks.
That requires a native app. This page uses what it genuinely can read, and infers
network density from how congested your connection is.
—
estimated nearby networks
waiting
—connection
—system RTT
—measured ping
—Mbps down
▶ what does WiFi density tell you?
Each WiFi access point covers roughly 10–50 metres indoors, or up to 100 metres outdoors.
In a rural area, you might see 0–2 networks. In a dense urban area, 30–80+ networks are normal.
Office buildings and airports can have hundreds of corporate SSIDs.
The density pattern alone reveals your environment type:
0–3 networks: rural, open outdoor, or very isolated building
4–10 networks: suburban residential, small business
11–25 networks: dense residential, small office building
26–60 networks: urban apartment block, commercial district
60+ networks: shopping centre, office tower, dense urban core
WiFi positioning (without GPS) is accurate to 10–20 metres in dense urban environments — better
than GPS in some cities, because the network database is precise and doesn't suffer from multipath.