Timo Arnall, Jørn Knutsen and Einar Sneve Martinussen. Runtime 4:44 This project explores the invisible terrain of WiFi networks in urban spaces by light painting signal strength in long-exposure photographs. A four-metre tall measuring rod with 80 points of light reveals cross-sections through WiFi networks using a photographic technique called light-painting. This builds on a technique that was invented for the 2009 film ‘Immaterials: the Ghost in the Field’ which probed the edges of the invisible fields that surround RFID readers and tags in the world. It also began a series of investigations into what Matt Jones richly summarised as ‘Immaterials’. While we were mapping out tiny RFID fields, we wondered what it would be like to apply the light painting process to larger-scale fields of Bluetooth, WiFi, GSM and 3G. What if we built huge light painting apparatus that could map out architectural and city-scale networks in the places and spaces they inhabited? We’re still very interested in understanding radio and wireless networks as one of the substrates essential to contemporary design practice. We built the WiFi measuring rod, a 4-metre tall probe containing 80 lights that respond to the Received Signal Strength (RSSI) of a particular WiFi network. When we walk through architectural, urban spaces with this probe, while taking long-exposure photographs, we visualise the cross-sections, or strata, of WiFi signal strength, situated within photographic urban scenes. The cross-sections are an abstraction of WiFi signal strength, a line graph of RSSI across physical space. Although it can be used to determine actual signal strength at a given point, it is much more interesting as a way of seeing the overall pattern, the relative peaks and the troughs situated in the surrounding physical space. After a week of walking through urban spaces holding and photographing this instrument, we have a much better sense of the qualities of WiFi in urban spaces, its random crackles, bright and dim spots, its reaction to the massing of buildings, and its broad reach through open areas. The resulting images show some of these qualities, and light painting is a brilliant medium for situating visualisations and data into physical world locations and situations. Timo Arnall is co-founder of Ottica, working with design, product invention, filmmaking, photography and strategy, most recently working with Google ATAP. His design, photography and filmmaking work is about developing and explaining emerging technologies through visual experiments, films, visualisations, speculative products and interfaces. He led the international research project ‘Touch’ investigating physical interaction with everyday objects. He has a Phd in interaction design. Over 15 years he has directed commercials, animated films, designed exhibitions and urban screens and architected web and mobile applications. Recent exhibitions include MoMA’s ‘Talk to Me‘, the V&A’s ‘Power of Making‘, Designs of the year at the Design Museum, London Transport’s ‘Sense and the City‘, ‘Invisible Fields‘ and ‘Habitar‘ at Laboral in Spain.