USGS maps show the UTM (Universal Transverse Mercator) grid. This rectangular grid has coordinates in meters, in false easting from the central meridian of a 6° zone (numbered starting with 1 at 177°W and proceeding eastward) and in northing.
Coordinates in meters require 6 digits for the easting and 7 digits for the northing. The grid labeled on the large scale (1:24,000) maps have the last three digits (0's) left off; the labels are thus for km rather than meters. Some maps have the UTM grid shown with a fine black line; it is labeled with 1 (easting) or 2 (northing) small superscript numbers followed by two larger numbers. Other maps do not show the grid, but have the ticks to create it shown in blue along the margins of the map, along with the grid labels.
| UTM ticks, in blue, on the top of a
The left tick shows the full false easting (373000mE), and the one to the right shows only digits needed to get 1 km accuracy. Two of the digits are larger than the others.
On military maps and for MGRS only the large digits (73 and 74) would be shown.
The grid labeled on the small scale (1:250,000) maps has the last four digits (0's) left off; the labels are thus for 10's of km rather than meters. These maps have the UTM grid shown with a fine black line; it is labeled with 1 (easting) or 2 (northing) small superscript numbers followed by one larger number.
One corner of the map will have the full coordinates in meters. Do not confuse the UTM grid with the state plane coordinates in feet, which may also be shown on the map margins.
Reading coordinates is a matter of interpolating between the grid lines (and perhaps first having to draw the grid lines, using a long straight edge and the ticks on the margins of the map). Special scales are available for this task, but a 3x5 card works well and can be properly marked using the scale bar on the map. Insure that you read values and record them to meters.
The UTM grid does not necessarily run north-south (as defined by latitude-longitude) and may be crooked, depending on the map projection used.
MGRS vs UTM.
Last revision 8/18/2009