Coordinates

If coordinates are to be passed on to another person it is technically necessary to report the horizontal datum and the latitude/longitude of the point (e.g. NAD 27 CONUS, 44 degrees, 7 minutes, 30 seconds north/ 104 degrees, 15 minutes, 10 seconds west...
The State Plane Coordinate System (SPCS) is a plane coordinate system (N-S and E-W lines are perpendicular) in which each individual state has from one to six zones, depending on the state's size and shape. The grid system in some states is based on the...
Generally, for the conterminous United States, the North American Datum (NAD) shift amounts to about 210 meters. This shift occurs because of the change in shape of the spheroid used to define the datum. The GRS 80 spheroid (used for NAD 83) is shorter...
UTM is the acronym for Universal Transverse Mercator, a plane coordinate grid system named for the map projection on which it is based (Transverse Mercator). The UTM system consists of 60 zones, each 6-degrees of longitude in width. The zones are...
One system is no more or less accurate than the other. They are just two different ways of positioning a point. Many experienced users prefer UTM over latitude/longitude when using 7.5' topographic quadrangle maps. Ocean going sailors and other marine...
Most survey marks were set by the US Coast & Geodetic Survey (now called the National Geodetic Survey) and information for those marks is available on the web. For further assistance call 301-713-3242 or e-mail infocenter@ngs.noaa.gov. If the...
Instructions for downloading from The National Map Viewer are located in a Download and Cart user guide. Orthoimagery is downloaded with the following steps:Zoom to area of interest.Click on Download Data tool.Draw a bounding box; choose a reference area...
Each National Aerial Photography Program (NAPP) frame covers a 5-by-5 mile area at 1:40,000 scale. Each National High Altitude Photography (NHAP) color infrared (CIR) frame covers an 8-by-8 mile area at 1:58,000 scale. Each NHAP black-and-white (B/W)...
We generally emphasize the following four points:a) Select a coordinate system (also called a "position format") you feel comfortable using. We suggest using Universal Transverse Mercator (UTM) or latitude/longitude. Most users find UTM coordinates ...
Focal length is the distance from the middle of the camera lens to the focal plane (i.e. the film). As focal length increases, image distortion decreases. The focal length is precisely measured when the camera is calibrated. Knowledge of the focal length...