Webrings - Maps - Trolleys and More
Thursday, December 29, 2016
Problem Solved: Can you patch this up?
Several post ago I mentioned about that mysterious line in the altitude map of western Brooklyn to Coney Island. From the info below, it seems that the altitude information comes from photographs that were patched together. Look, it is better than nothing! The map below was produced with ARCGIS and the earlier maps were produced by QGIS. I assume that this aerial map source as used to derive surface elevation because the seams happen to be in the right places as described before.
he National High Altitude Photography (NHAP)
program was coordinated by the USGS as an interagency project to acquire
cloud-free aerial photographs at an altitude of 40,000 feet above mean terrain
elevation. Two different camera systems were used to obtain simultaneous
coverage of black-and-white (BW) and color infrared (CIR) aerial photographs
over the conterminous United States. The color-infrared photographs were taken
with an 8.25-inch focal length lens and are at a scale of 1:58,000. The
black-and-white photographs were taken with a 6-inch focal length lens and are
at a scale of 1:80,000. The NHAP program, which was operational from 1980 to
1989, consists of approximately 500,000 images. Photographs were acquired on
9-inch film and centered over USGS 7.5-minute quadrangles.
In the first map below, the second map below was georeferenced using ARCGIS. I did not do a very good job of it and you can see that the transit lines are ghosted. At any rate, once the map is geo referenced, you can bring in any data layer. I brought in the altitude contour line (vector file) in pink and you can see the abnormality follows the aerial photograph's seam line in about the same position that we mentioned before.