Star-Bulletin Features

Monday, April 23, 2001

A lunar landing pod? Not even close. Most
people walk on these every day!


The sidewalk secrets
that lie beneath your feet

There is a whole world underfoot, and you are walking all over it! For the next couple of weeks, we will be identifying -- or trying to identify -- those little markings and mysterious artifacts attached to our city pathways and streets. It is the Secret Life of the Sidewalk.

Our first candidate is the smallest and is frequently overlooked. It appears to be a nail head driven into the sidewalk. It is often surrounded by a white circle painted on the concrete, and sometimes there are numbers painted nearby.

According to Jerry Iwata, the head surveyor at the city's design and construction division, the mystery objects look like nail heads because that's what they are. "They're concrete nails, more robust than regular nails, but pounded right into the sidewalk," said Iwata.

They are used as reference points for surveyors. Surveyors set up their plumb bobs and sighting tools over the pre-mapped point assuring themselves that the next time they return, their measurements will be the same.

The one we photographed here reads "AGM" atop the head. Others we saw said "PK" or were blank. What does that mean? There is a well-known Canadian survey company named Archibald, Gray and McKay that goes by that acronym, and surveying links online often make reference to AGMs or "above-ground markers."

But Iwata has a simpler explanation.

"It's just the brand of nail. The city uses PK-brand nails," he said. And no, surveyors do not need permission to pound nails into city property, he added, as long as safety procedures are followed. Presumably, that includes not hammering your thumb.

Burl Burlingame

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