I've seen signs along the roads leading to San Diego stating that the elevation is 11 feet. Exactly where is the spot where the measurement was taken? Or is it an average elevation: And who gives a darn anyway?
-- Bruce W., La Mesa
Don't be misled just because it's painted on a sign. "San Diego: elevation 11 feet" seems to be a factlet without a source. At least a source that anyone can identify. A check with the offices of the city and county surveyors drew a blank, so we'll have to work with best guesses. First of all, the elevation, whatever its source, is undoubtedly a single-point reference. Deriving a reliable average elevation in the city would be tough, given our up-and-down terrain. A lot of work for a figure nobody much cares about. We're close enough to actually view sea level, so a foot more or less isn't going to make a difference.
Odds are that our elevation was measured at city hall or Horton Plaza, Santa Fe station, or other civic landmark. This is a long-time tradition dating back at least to the days when railroad surveyors marked up the Midwest and West during the mid-1800s. An elevation for a town in Iowa or the Rockies, where there would be no sea level visible for reference, would have more practical value for residents and especially railroad builders than does an elevation for a coastal city like San Diego. But because elevation is a traditional descriptor for a city, San Diego would have it's height measured just like Des Moines or Denver. The county surveyor's office holds topographical maps one by U.S. government geologists that date back to 1848, and there's a chance that the 11-foot measure derives from such a source; but it still would be a single-point reference from one of several benchmarks around the city.
As for how the unknown surveyor arrived at 11 feet, its likely that it was done with an altimeter, depending on how long ago the measure was taken, just like an airplane's altitude reckoning device. But the fact is inescapable that nobody much cares, so that 11-foot figure will probably remain on the signs until the big one finally hits and they change the sign to read, "San Diego: elevation -100 feet."