Oh, they've done dirt (particles) before. There was that time where Joseph had to escape from the stand that grew on his arm by sucking blood. He mapped out some tar or something in dirt while he fell.
The new thing that happened this time though, was that by showing Mariah's movements in real-time he upgraded the map to GPS.
How scary was mistaking the old lady's "amazing legs" though? Leggings are now the most deceptive thing next to makeup and corsets.