Every UTM longitude zone has a particular Cartesian coordinate system associated with it (i.e., a local xy coordinate system). The UTM easting and northing coordinates are the x and y coordinates, respectively, of this system.
UTM easting and northing coordinates are numerical, and are reported as base-ten integers (Arabic numerals, no decimals or fractions). The numerical values are written without commas, spaces, or decimal points; and in non-exponential notation (e.g., neither in engineering notation nor in scientific notation). The coordinate definitions (see below) imply that the numerical values are nonnegative. Therefore, the coordinates are written as unsigned numbers (i.e., without “+” or “−” signs).
UTM easting and northing coordinates are reported in units of meters. Some non-technical publications on civilian navigation and the GPS use a nonstandard convention in which the easting and northing coordinates are reported in kilometers, but the use of kilometers doesn’t conform to the standard defined by DMA [1989] and therefore isn’t recommended.
Table 2.3: Minimum and Maximum UTM Easting Coordinates
Latitude
Horizontal UTM Easting Coordinates
Datum (meters)
Minimum Maximum Difference
NAD 27 166 018 833 982 667 964 0◦N./S. NAD 83 166 022 833 978 667 956 NAD 27 441 866 558 134 116 268 80◦N./S. NAD 83 441 868 558 132 116 264 NAD 27 465 004 534 996 69 992 84◦N./S. NAD 83 465 006 534 994 69 988
Source: Decimal values of minimum and maximum easting coordinates were obtained from National Geodetic Survey [2007], and then were rounded up and down, respectively, to the nearest integer coordinate corresponding to points within a UTM longitude zone.
2.3.1 Easting Coordinates
The easting (x) coordinate increases continuously as one moves eastward. Each longitude zone has a central meridian midway between its two bounding meridians (See Figure2.7). The central meridian of each longitude zone is assigned the easting coordinate 500000m (i.e., x = 500 000 m). Consequently, the easting coordinate has the following characteristics:
• It’s local to the corresponding particular longitude zone; • It’s non-negative; and
• It’s also referred to as false easting.
Table2.3 lists the minimum and maximum UTM easting coordinates for regular (6◦ wide) UTM longitude zones, at various latitudes and for the two most commonly used datums in the U.S. The full range is realized only at the equator, where the UTM longitude zones are widest. At higher latitudes the range generally is narrower, because the UTM longitude zones narrow with increasing latitude due to convergence of the meridians.
The ranges in Table2.3correspond to regular UTM longitude zones; for irregular zones the ranges differ from these. From these results it follows that the UTM easting coordinate of every point within every regular UTM longitude zone is a six-digit integer. It turns out that this is also true for irregular UTM longitude zones (see Appendix A).
2.3.2 Northing Coordinates
The northing (y) coordinate increases continuously as one moves northward. In the northern hemisphere the equator is assigned the northing coordinate 0mN (i.e., y = 0 m). In the southern
Table 2.4: Minimum and Maximum UTM Northing Coordinates
Hemisphere
Horizontal UTM Northing Coordinates
Datum (meters)
Minimum Maximum Difference
NAD 27 0 9 328 895 9 328 895 Northern NAD 83 0 9 329 005 9 329 005 NAD 27 1 117 046 10 000 000 8 882 954 Southern NAD 83 1 116 916 10 000 000 8 883 084
Source: Decimal values of minimum and maximum northing coordinates were obtained from National Geodetic Survey [2007], and then were rounded up and down, respectively, to the nearest integer coordinate corresponding to points within a UTM longitude zone.
hemisphere the equator is assigned the northing coordinate 10000000mN (i.e., y = 10 000 000 m). Consequently the northing coordinate has the following characteristics:
• It’s local to the corresponding particular hemisphere.
• It’s non-negative.
• It’s also referred to as false northing.
Table2.4 lists the minimum and maximum UTM northing coordinates for any given UTM longitude zone, for the two most commonly used datums in the U.S. The full range isn’t realized near the bounding meridians of each zone, due to meridian convergence. From these results it follows that the UTM northing coordinate of every point within every UTM longitude zone is a one- to seven-digit integer (see Appendix Balso).
2.3.3 Easting and Northing Coordinate Specifications
The conventional format for reporting UTM easting and northing coordinates is rather specific. The numerical value of the coordinate is written first (leftmost), immediately followed by the lowercase “m” abbreviation for meters, with or without a single space separating the two. An uppercase “E” or “N” immediately follows the “m”, to indicate whether the coordinate is an easting or a northing, respectively. The following examples illustrate the convention.
Examples: Conventional Format for Reporting UTM Easting Coordinates
“500000mE” or “500000 mE” (e.g., the central meridian)
“566785mE” or “566785 mE”
“177003mE” or “177003 mE”
“792324mE” or “792324 mE”
Examples: Conventional Format for Reporting UTM Northing Coordinates
“0mN” or “0 mN” (e.g., the equator)
“353mN” or “353 mN”
“8315466mN” or “8315466 mN”
“10000000mN” or “10000000 mN” (e.g., the equator)
2.3.4 Coordinate Gridlines
Within each UTM longitude zone, two sets of gridlines are defined – a set of UTM easting gridlines and a set of UTM northing gridlines. The easting gridlines are orthogonal to the northing gridlines. Each set is described below.
Within each UTM longitude zone, the UTM easting gridlines form a set of contour lines. Each UTM easting gridline connects those points on the earth’s surface that have the same UTM easting coordinate. The easting gridline corresponding to 500 000 mE (i.e., the central meridian) extends from 80◦S. lat. to 84◦N. lat. As one moves poleward from the equator, each longitude zone becomes narrower, so the easting gridlines corresponding to the more extreme easting coordinates don’t extend as far poleward as the central meridian does (see Figure2.7). Rather, these easting gridlines only extend northward to the points where they intersect the zone’s bounding meridians. Within any particular UTM longitude zone, the easting gridlines never intersect.
Within any particular UTM longitude zone, the UTM northing gridlines also form a set of contour lines. Each UTM northing gridline connects those points on the earth’s surface that have the same UTM northing coordinate. The northing gridlines within each longitude zone extend from one bounding meridian to the other, across 6◦ of longitude. As one moves poleward from the equator, the longitude zones become narrower, so the northing gridlines become shorter (see Figure2.7). Within any particular UTM longitude zone, the northing gridlines never intersect.