Some UTM northing values are valid both north and south of the equator. In order to avoid confusion the full coordinate needs to specify if the location is north or south of the equator. Usually this is done by including the letter for the latitude band.
If this is your first exposure to the UTM coordinate system you may find the layout of zones to be confusing. In most land navigation situations the area of interest is much smaller than a zone. The notion of a zone falls away and we are left with a simple rectangular coordinate system to use with our large scale maps. Why then is it being used by surveyors and allied specialists, while there are other projections -conical, orthogonal- and others. Take a look at compromise map projections. Since a UTM zone is a projection onto a strip of a cylinder, which is flattened out to a planar strip, grid north cannot be true north except at the central meridian.
Consider this: For each zone, the central meridian passes through the North and South Poles. The amount of deviation increases with distance from the central meridian. You did a good job of describing distance distortion. I have not found any good references regarding direction distortion.
Close, but not quite. First, the UTM System is not a projection!!! TRY: Distortion is small near the central meridian, decreases as you approach a standard circle, and then increases and worsens as you move beyond the standard circle and toward the edge of the zone. Your email address will not be published.
Do all USGS 7. Historical Topographic Map Collection : Through time, policies have changed regarding whether or not a full UTM grid would appear on the 7. Beginning in the mid s, the grid was indicated by blue ticks around the map at 1,meter spacing.
In , the ticks were replaced with a full-line black The UTM Universal Transverse Mercator coordinate system divides the world into sixty north-south zones, each 6 degrees of longitude wide. UTM zones are numbered consecutively beginning with Zone 1, which includes the westernmost point of Alaska, and progress eastward to Zone 19, which includes Maine.
Why don't U. Filter Total Items: 4. Year Published: Map Scales The proportion chosen for a particular map is its scale. View Citation. Geological Survey. Year Published: Map projections: A working manual After decades of using only one map projection, the Polyconic, for its mapping program, the U. In a conformal projection local angles are preserved and shapes are represented accurately and without distortion for small areas.
As a result of preserving angles and shapes, area or size of features are distorted in these maps. As mentioned, choosing a secant projection and a narrow zone minimizes the distortions in a map generated from UTM projection. The 20 bands are labeled with letters, beginning with C and ending with X from south to north. Letters I and O are omitted to prevent confusion with numbers one and zero.
Note that letter N designates the first latitude band above the equator, so any letter of alphabet after N refers to a band in northern hemisphere and any letter before N refers to a band in southern hemisphere. To specify a UTM grid zone, the zone number column is given before the zone letter row , such as Zone 11U.
Since UTM zones are bounded by lines of longitude and these lines converge towards the poles, consequently the width of each zone tapers narrows from the equator towards the poles. However, there are exemptions, where dimensions of some zones are adjusted. As a result zones 32X, 34X and 36X have been omitted.
By means of a map projection, the earth's curved surface is transformed to a flat two-dimensional surface. A coordinate system or grid is superimposed on the resulting flat surface.
Such a coordinate system provides a referencing frame in order to define the position of objects. Universal Transverse Mercator is a projected coordinate system , which is a type of plane rectangular coordinate system also called Cartesian coordinate system.
In the two-dimensional surface, two straight lines intersect each other at right angles. These lines are called the axes, and their point of intersection is defined as the origin 0, 0 of the coordinate system. The horizontal axis east-west is labeled as x-axis and the vertical axis north-south as y-axis. The position of a point in the rectangular coordinate system is defined by its distance from the x and y axes.
The two distance values are the x and y coordinates of the point, and use a measurement unit such as meters, feet, etc. The intersection of the x and y axes in the rectangular coordinate system divides the space into four quadrants. Points along a vertical grid line to the right of y-axis have a positive x coordinate value while those to the left of y-axis have a negative x coordinate value.
Points on a horizontal line above the x-axis have positive y coordinate value while those below x-axis are given negative y value. Therefore a point lying in the first quadrant, to the right of y-axis and above x-axis, has positive x and y coordinate values. In contrast to the projected coordinate system, the geographic coordinate system uses curved grids in order to accommodate the curved surface of the earth; and the geographic latitude, longitude coordinates are measured in degrees, minutes and seconds of arc.
These geographic coordinates are converted to plane coordinates by means of map projections. The UTM coordinate system is a universally used plane coordinate system except for polar regions.
UTM zones are "flattened" using the Transverse Mercator projection, and a rectangular grid network of straight horizontal and vertical lines is superimposed on each zone. Although meridians inside the zone and on zone boundaries converge towards the poles, vertical grid lines are oriented parallel to the central meridian of each zone and make an angle to the other meridians.
Horizontal lines in turn are parallel to the equator. As a result the grid squares stay the same size and shape throughout the map. The vertical direction of grid lines is referred to as grid north on maps, as opposed to true north which is associated with the direction of meridians or lines of longitude.
The angular difference between grid north and true north is referred to as grid declination , and is sometimes indicated on the map margin along with magnetic declination. For large scale maps this difference is small and is usually not taken into account in map reading. In the UTM grid layout, the unit of measurement is meters , and the coordinates of a point are designated as easting determine east-west position and northing determine north-south position.
Vertical grid lines on map are used to find easting while horizontal grid lines are used to find northing of a point; similarly grid lines can be used to help locate a point with known coordinates. Designation of the central meridian as the reference y-axis i.
For this reason, the central meridian is assigned an arbitrary value of meters, thus avoiding any negative easting coordinates; points lying to the east of it would have an easting value greater than m and points lying to the west would have a value less than m. This assignment would place the origin outside the zone at m west of the central meridian, as a result the origin is called a false origin and the easting coordinates are referred to as false easting.
The equator is designated as the horizontal reference axis for UTM northing coordinates and is assigned a value of 0 meters North for zones in northern hemisphere.
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