It is perhaps not surprising that the ancient Greeks had a word for writing on walls (τοιχογραφία from τοῖχος ‘wall’ and γραφία ‘writing’) but apparently no word for writing on streets or sidewalks—no *‘οδογραφία (from ‘οδός ‘road’) or *πεζοδρομιογραφία (from much later Greek πεζοδρόμιο ‘sidewalk’ itself from Doric πέζα ‘foot’ and δρόμος ‘(race) course’). There are at least two reasons for these lexicographical lacunae: (1) the ancient Greek roads didn’t provide a suitable surface for writing and (2) why, before the invention of hopscotch, would anybody want to write on the ground when you could write on a wall without having to bend over?

Modern times have brought us both the necessary canvases—reasonably smoothly paved streets and sidewalks—and ample reason to write on them, not so much in the pursuit of individual artistic expression (though this is not unknown) but in the more mundane interests of public safety: Marks on the pavement can warn you of the location of the public utilities’ underground pipes and ducts, which is a good thing to know before you begin excavation for that new condo development or lawn sprinkler system.

The conventional term for these marks is mark-outs, a sampling of which at a local construction site is shown in figure 1:

four utilities

figure 1

Mark-outs are color-coded according to the conventions promulgated by the American Public Works Association and Dig Safe System, Inc.,“a free service, funded solely by its utility members to promote public safety and avoid costly underground utility damage,” which state law requires its public utilities such as gas, electric, cable TV, and regulated water companies to join. Dig Safe facilitates communication among the various utilities and construction companies to keep them from stepping on each other’s toes (or underground pipes and cables).

The contractor “premarks” the intended work area with white spray paint using a special spray can that works upside down and has a vertical nozzle and a long handled trigger, which allows the writer to work while standing:

Dig Safe mark-out

figure 2

Here, a construction company whose initials are JFW has announced its plan to dig after notifying Dig Safe. The notification covers fading gas and cable(?) company mark-outs from previous construction at the site. The MBTA has marked its electric line (for the trolley) after Dig Safe has given the go-ahead.

We know that the MBTA marking is for an electric line because it’s in red. Such markings typically contain additional information:

Electric company mark-outs

figure 3

The leftmost panel’s single arrow and letter E (which sometimes looks like a W or an M or an indecipherable squiggle, depending on the writer’s spraypaintsmanship) say that we’re dealing with a single electrical cable. The middle panel may be decoded as a diamond between parallel lines, signifying a multiple duct structure, and the rightmost H figure denotes multiple buried cables. These details are largely handed down via the oral tradition and are not usually documented.

The other standard color codes, besides red for electric, are pink for temporary survey markings; blue for potable water; green for sewers and drains; purple for reclaimed water, slurry and irrigation lines; orange for cable, communication, alarm, and signal lines; and yellow for gas, oil, and steam. In the case of the overloaded orange and yellow, the writer may include disambiguating information. For example, the yellow mark-out in figure 1 tells us that what’s underground is a two-inch (2”) steel (ST) gas line, while the one in figure 4 tells us that the gas company is National Grid and the pipe is cast iron (CI):

Gas company mark-out

figure 4

These same color codes are used in the little flags that go where spray paint cannot (or should not) go to mark underground pipes and cables

Mark-out flags

figure 5

and in the flagging tape and triangles that serve as surveyors’ reference marks:

Survey marker

figure 6

Special thanks to Edward Goldfrank for his substantial contributions to this posting.