An out-of-control ticktacktoe game

Dear Matthew Alice: A large, white, official-looking X has been painted in the bike lane on northbound 101 in Encinitas, in front of D.B. Hacker’s restaurant (101 North Highway 101). Who painted this X, and what are its implications? . — A.G., North County

The ominous X is an aerial marker. It was painted by a surveyor, who also pounded that shiny nail into the asphalt at the intersection of the two arms of the X. Somewhere in the vicinity (maybe within blocks, maybe within acres or miles) are three more Xs with nails, and the four Xs mark the corners of a square or rectangular chunk of land. The nails indicate points of known elevation and map coordinates.

When the first surveyor’s done, an aerial surveyor hops in a plane and takes a series of overlapping photos of the land chunk in question, making sure the Xs are included. When the photos are assembled, all the landmarks can be located correctly and their elevations described using the Xs as reference points. (I’ll spare you the details. It’s complicated.) After that, who knows. Sometimes the surveys are used for mapping. Sometimes they mean we’re in for a new strip mall or housing development. Around the corner from Hackers, on Second, west of Highway 101, you’ll see two more bike-lane Xs from two other projects. The county is lousy with them, like an out-of-control ticktacktoe game.