National Geographic : 1956 Mar
An IAGS Student Practices Surveying on a Photograph To help Latin Americans make accurate maps of their own countries, IAGS main tains a cartographic school in the Panama Canal Zone. Here in the last three years 227 students from 17 countries have learned subjects like geodetic surveying, astronomy, photogrammetry, drafting, and map reproduction. Apprentice cartographers practice on all sorts of instru ments. Student Angel Lujan of Peru uses a Wilson photo alidade to measure angles be tween points in the photo graph exactly as if he were on the spot where the camera stood. times by thousands of feet. This apparent error is not the fault of the engineer or his instruments, but of the earth itself. Before he looks at the stars, the surveyor carefully levels his instrument so that he will know at just what angle it is pointing into the sky. His leveling, of course, is always done in reference to the ground beneath his feet and to the pull of gravity. Any irregularity in the earth's surface at or near his Laplace station makes itself known as what scientists call a "gravity anomaly," which means simply that the direction of gravity's pull at that spot is deflected from the vertical. This, of course, spoils the sur veyor's aim with his telescope and causes an error in his calculations when he determines his latitude and longitude. The amount and direction of this error are what the geodesists need to know in order to figure out the shape of the earth. Working back ward, they can calculate just what kind of a kink or bulge in the geoid must have caused it. And using data from hundreds of La place stations in a line stretching nearly from pole to pole, they will end up with an accurate picture of the earth's over-all curva ture. "An important thing to remember about the IAGS," Colonel Robertson told me, after I had seen its work going on in five countries, "is that we are not mapping Latin America. We're helping the Latin Americans to do it them selves. It's their program. We offer sug gestions, we lend equipment and give techni cal advice. The rest is up to them. "You get our engineers working with Chil ean or Colombian or Guatemalan or any other Latin American engineers and they become friends. They stick together on a project for months or years and really get to know each other. Our men learn Spanish, the others learn English. They get to like each other and, even more important, they come to re spect each other. "Imagine this going on in 17 countries, on half a dozen or more projects in each country, year after year. You can see what a terrific thing it is for furthering inter-American rela tions."