I wonder about the specifics of how the data was filtered?
I ran the app since it was announced, and was anticipating seeing the map. I noticed a few little quirks. I can see a single spot of 2G centred on home in on our part of town which is otherwise 3g. I'm guessing that's due to the app logging a 2g signal when I'm home (in fact most of the time the phone is roaming from t-mob to orange at home).
Also, areas where I had driven (Strines Road from Penistone in particular), show no data, yet I'd driven that route twice since installing the app, so I'm wondering if they filter out values unless there's a enough points. Annoying in rural areas, where there haven't been that many data points logged, as even some data is better than nothing.