Yes, there are (eg. wigle.net, mostly based around wifi, but also scans cell towers), but the data is very noisy, since every phone is different and everyone wears it differently (if you wear it higher, in a shirt pocket, you'll get higher signal levels than if you carry it in a pants pocket, or in your hand, or if you have an old iphone, if you're holding it in your left hand instead of the right).