Video: Tag along with a RootMetrics’ tester as he maps Chicago’s mobile networks

Luke Metz spends a lot of time hanging out Dunkin’ Donuts(s dnkn) and Wal-Mart(s wmt) at odd hours. If you ever see him loitering with a cup a coffee in his hand in your town, he’ll probably be carrying a very conspicuous-looking portfolio case crammed full of smartphones.

Don’t worry, he isn’t up to anything illegal or creepy. Rather he works for mobile testing outfit RootMetrics. He’s running network tests on all four of the major carriers mobile networks, using an array of smartphones. Metz isn’t just taking a signal measurement here and running a speed test there. He’s recording thousand of individual data points each hour as he crisscrosses the week’s chosen city in a rental car, following a randomly generated path over highways, side streets and ultimately into stores, pharmacies, restaurants and building lobbies.

After a week or two or three – depending on the size of the market – he packs up his gear and moves to the next town. The measurements he collects will then go into the Seattle startup’s databases along with millions of data-points collected from consumers using Root’s crowdsourced testing app.

On Thursday, RootMetrics released its in-depth report on the performance of Chicago’s networks (Verizon(s vz)(s vod) took the overall prize). Metz was part of a team that took the measurements for that report back in November, and they invited us along to get a first-hand perspective on how he does his work. Of course we brought along a camera.