For over two hundred years, land has been New York City’s most valuable resource. The best evidence of this is the last decade’s skyrocketing rents. Rent, being the price of using real estate, is the market’s measure of the value of land. And, as Mark Twain quipped about land, “they’re not making it any more.”

Parenthetically, Twain was wrong. New Yorkers have created real estate for centuries. Roughly one-third of downtown Manhattan is now landfill. Brooklyn’s Red Hook was an island before the dredgings from Erie Basin transformed it to a peninsula.

Increasing land values also lead landowners to change the uses of their property to maximize profits, dramatically illustrated by agriculture’s near-disappearance from the City’s economy. As late as 1900, the City had over 2,000 farms averaging 25 acres – over 78 square miles of agricultural land.

Then the construction of railways, subways, and trolley lines into the outer boroughs put the countryside within commuting distance of downtown. Developers began buying open land for new housing. This increased the value of the remaining farmland, and the taxes levied on it. More sales followed. By 1930, about 200 farms remained; by 1980, only 15.

Oddly, the Census Bureau reports that the number of farms in the five boroughs increased to 23 in 2002, the most recent date for which statistics are available. But most were farms only in a legal sense, being greenhouses for trees, flowers, and houseplants.

The present condition of Manhattan in particular makes one wonder what the island looked like before we began mucking with it. Fortunately, as even colonization involves land use, requiring surveying, measurement, and mapping, the landscape has been carefully recorded since the early 17th century.

Old Manhattan’s most important map lies, appropriately enough, in custody of the Manhattan Borough President. Drawn in 1820 by John Randel Jr., who had been chief engineer and surveyor for the board of street commissioners authorized in 1807 to organize the city’s streets, the Randel Farm Map was part of Manhattan’s most important planning: the street grid.

I saw the map about 25 years ago. I was gossiping about politics with Harry Kleiderman, a friend who worked in the borough president’s office. Suddenly, he asked whether I wanted to see the Randel Map. Without waiting for an answer (I didn’t know what the Map was), Harry reverently opened a large steel cabinet. Drawn to a scale of one inch to 100 feet, the map had been created on heavy lined cloth, carefully divided, and each part mounted on rollers to prevent cracking along fold lines. It was called a Farm Map as a term of art, literally referring to a map that delineates farms and estates in a semi-rural area.