What now is a free, useful service to New Yorkers may shortly become an “incredibly targeted” advertising vehicle.

We’re talking feet, here. Feet.

You want to go slumming from your Park Avenue pied-a-terre to a newly discovered little bistro in the West Village and the limo is in the shop? Check out the subway directions at www.HopStop.com, and in seconds you will have subway stops and transfers, plus a map, and an estimate on how long it will take you, in fractions of a minute, to walk from the stop right to the sommelier’s desk.

The quick and free service was started last fall by Park Avenue-based Chinedu Echeruo, a Nigerian-born Harvard MBA who says he got lost too many times. The site isn’t making a dime yet. But HopStop has a plan.

“The strategy is to drive up usage, iron out all the technology, and then go out to the advertisers in a position of strength,” said Bill Raffo, HopStop’s spokesman.

HopStop will attempt to bring in the advertising by telling people like restaurant owners that their ads will be seen only by folks who have asked how to go to their immediate neighborhood in the first place.

HopStop is continuing to update. Among the newest features: it is available in seven languages; with word recognition users don’t need specific addresses for most famous places like museums and airports – and even some famous restaurants.

Users can text message themselves the directions straight from the website, eliminating the need to carry around paper, and a new mobile service allows users to call on the run and get directions on their cells.

You have to sign up for that last one, which is kind of like admitting you’re going to get lost.

But it’s free.