Mapping the World via Cellphones

Here at OpenSignal we’re using cellphones to map signal, cell towers & Wi-Fi access points. When we launched back in 2010 these seemed like obvious things to map using cellphones. To our astonishment we’ve built the biggest project of its kind, with close to 3m app downloads and billions of readings collected; data we’re using to help consumers make the right choices about cellphone networks. But wireless data is far from the only thing that can be collected and mapped using cellphones.


A recent project by Dutch Meteorological Researchers, with which we had the pleasure of being marginally involved by providing some data, constructed a rainmap of the Netherlands in unparalleled detail based on cellular network data. While the use of attenuation of electromagnetic signals to measure rain is not new – rain radar has made of this technique for many years, this is the first time that cellular data has been used instead of dedicated infrastructure. The principle is simple, certain radio frequencies suffer significant drops in intensity as they pass through precipitation, the greater the volume of water falling the greater the drop.

It is important to note that the researchers – Aart Overeem Hidde Leijnse, and Remko Uijlenhoet – used link data; signals sent between cell towers themselves rather than from phone to tower, the latter frequencies being much less subject to attenuation. A nice feature of link data is that is collected and stored automatically by the cellphone networks. It’s also relatively high resolution – for example there are 325 rain gauges in the Netherlands that are measured daily and 32 that are measured every 10 minutes. Overeem et al. calculated the precipitation across 8000 link paths for 15 minutes intervals, meaning that they collected over 150 times as many data points on a daily basis.

Why it’s important

The higher the dependence of a country’s economy on agriculture, the greater the need to have accurate maps of precipitation. Unfortunately these are often the economies least able to afford the installation of rain radar or to even manage a comprehensive network of manual measurement gauges. A further advantage of this approach is that it does not rely on smartphones, as all the data is provided by the cellular infrastructure irrespective of device type.

No Going Back: The Addition of Sensors to the Galaxy S Series of Phones

From a post of mine on BigDataRepublic: the addition of ever more sensors allows for new possibilities for crowd-sourcing data, especially when those sensors are repurposed.


Sticking with the weather theme, barometers are becoming increasingly commonplace in cellphones and tablets, with Samsung their particular champion. They are being promoted as a means of improving location fixes, as they allow the calculation of altitude from a GPS fix that uses only 3 satellites (instead of 4), saving time and minimizing battery use. But these barometers can also be used for their most basic purpose: the measuring of pressure. This is being done by PressureNET

We’re keen to point out that OpenSignal were pioneers in this field, having built a prototype app for this purpose that won CrowdHack 2011 – as proof we have an engraved Gurkha sword that we’re trying to have mailed to us in the UK. Once signal is solved we might move back to weather, so watch this space… and in a few months click refresh.

Why it’s important

Pressure doesn’t just matter to David Bowie and Queen, it is the key factor in determining other weather conditions. A network of real-time pressure gauges could potentially open the door to hyper-localized weather prediction. Instead of looking at the weather in London for the afternoon, you’ll be looking up the weather on Trafalgar Square at 3.45pm – 3.50pm.


Here’s another example of what I call sensor repurposing – where a sensor introduced for one purpose (e.g. determining altitude) is used for another (reading pressure). The accelerometer plays a role in detecting what you’re doing with your phone, and is used as such by games like DoodleJump, but it can also be used to crowdsource tremor readings. For this purpose researchers have developed the CalTech Seismic Network which uses Android phones. Clearly, unless you can convince people to leave their phone lying flat, you’ll get a lot of noise, but that can be averaged away.

Why it’s important

The more we can do to understand earthquakes, the better. What is especially exciting about this project is that it could help form part of an early warning system. The more sensitive the detection network the greater the possibility that such a system could be realised. Obviously the benefits of an earthquake early warning system do not have to be innumerated here.


There are two possibilities here: one is to crowdsource locations of road users from devices – this is the approach favoured by Waze in creating their real-time traffic maps. In common with the rain mapping project above, the second approach uses data collected from the networks themselves and has been the subject of various academic studies and is commercialised by companies such as CellInt. The cellphone networks have data on which of their subscribers are connected to each of their towers at any point in time – they have this data even if the user is not using their phone, so long as they’re reachable via the cellphone network (not out of signal or in Airplane mode). While this may only give a crude estimate of location it can be very good for calculating what stretch of road a subscriber is on and their average speed of travel – as they can see the subscriber being passed (or “handed off”) from tower to tower.

Why it’s important

Current approaches relying on traffic cameras, helicopter traffic spotting and manually phoning in problems are painfully inefficient in comparison.

A run down of some other possibilities


What’s the average mobile phone screen size in Ulan Bator and how has it changed? What’s the most popular phone in New Delhi? The answers can be found by using technology to map technology.

Human Behavior

Which countries are most talkative, who sends the most SMS and where do people consume the most data? How do people move about? What apps are common across cultures? As cell phones consume more and more of our time, they are key to understanding our own behaviour. Mobile devices are poised to play the principal part in the nascent Quantified Self movement whereby people aim to empirically study and shape their own behavior for self-improvement.

Digital Literacy

A combination of measures – such as technology, density of Wi-Fi points, quality of networks (including presence or absence of 4G) to try to understand the state of digital infrastructure. Along with Ookla (makers of and the US Census Bureau, we contributed data to TechHive’s rundown of the top ten tech friendly US cities. Access to the internet is becoming as important as access to education, measures of digital infrastructure could accordingly be used to augment the UN’s Human Development Index.

From the dialer to apps to maps

For many, the dialer is now just one among many apps on our phones, and for some it’s hardly ever used. The smartphone has moved the mobile phone far beyond its simple telephonic functions, and turned it into the device through which we organise our lives. The possibilities afforded by phones extend far beyond the personal utility of apps, cell phones are not only the points by which we access so much of our world, they have a collective potential to improve our understanding of the natural and man-made world.

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