PDF of: Using the UTM Grid System to Record Historic Sites (2 MB)

by
Wilford P. Cole
1977

Forward
Acknowledgments
Introduction
The UTM Grid System
Using the System
  The Five Methods
  General Information
  UTM Representation of Extensive and Complicated Sites
    Complex Sites
    Unclosed Sites
    Discontinuous Sites
    Compound Sites
  Method I
  Method II
  Method III
    Version 1
    Version 2
  Method IV
  Method V
Rounding and the Degree of Precision
Digitizing
Computerizing UTM Data
Extended UTM Grids
Variant Forms of UTM Notation
Determination of 100-km Square Designations for the UTM Kilometer Grid System
Other USGS Map Series
Vocabulary
Figures, Charts, Graphs, etc.
Sources of Figures
List of All Publications

The Five Methods

This manual describes five methods for measuring the UTM reference for a point. The first two are the easiest and most common, and each has specific advantages in certain situations.

Method I, the simplest and least subject to mechanical errors, is best for measuring in simple situations, but is somewhat inconvenient for measuring a number of points widely scattered across a single map.

Method II is preferable for complicated situations, but requires, in addition to a straightedge and a coordinate counter, a drafting board and T-square or parallel rule. Carefully applied, however, either Method I or II will give satisfactory results on USGS maps drawn to common scales.

Method III may be applied to maps of any scale, that is, maps not represented on the coordinate counter, provided they have UTM tick marks or grid lines.

Method IV is designed for use on sites too near map edges to be measured by the first three methods.

Method V establishes UTM references on USGS quadrangle maps which lack UTM ticks.

General Information

1. UTM zone numbers appear in the legend in the lower left margin of modern USGS maps.

2. On these maps, blue tick marks around the margins set off intervals of a thousand, 5 thousand, or 10 thousand meters, depending on the map scale. To check this, use the metric scale printed at the center of the lower map margin. The easting and northing values of these ticks are printed on maps in an abbreviated form that shows values in thousand-meter units such as 177 or "23. These abbreviations are clarified near the northwest and southeast corners of the maps, where at least one tick value will be written out in full, to the nearest whole meter, for each map edge. For example, an easting abbreviated '23 would be printed in full as 523000mE, meaning 23,000 meters east of the central meridian. Similarly, an easting abbreviated as 177 would be printed in full as 477000mE, meaning 23,000 meters west of the central meridian for the zone in which the map is located. Remember that the central meridian always has an arbitrarily defined easting value of 500,000 meters.

3. Lines connecting UTM grid ticks of equal value are seldom parallel with lines of latitude and longitude, or with the edges of quadrangle maps. This is a result of the map projections used and the fact that longitude lines converge toward the poles, whereas UTM grid lines do not coverage. The effect becomes more evident as the distance from the central meridian in each zone increases. None of this noticeably affects the accuracy of measurement at common map scales.

4. When drawing lines between UTM grid tick marks, make the finest line possible. Use a very sharp, hard pencil or very fine pointed pen to draw connecting lines. Lines drawn with dull or soft pencils, or with felt markers, are too wide for precise measurement. Number 3 office pencils, and number 3H or 4H drafting pencils, if kept sharp, do a good job.

5. USGS has announced that new and newly revised quadrangle maps will have printed UTM grid lines, making it unnecessary to draw them by hand. It will take several years to reprint all of the USGS quadrangles, but as they are issued, the labor needed to measure UTM references will be reduced significantly.

6. The UTM coordinate counter (see figure 1) is used in all methods except Method III. It has measuring scales to match the common USGS map series around its edges and each corner of the counter corresponds to a different map scale.

Be sure to choose the correct scale for the desired measurement to be made. The organization of each measuring scale is the same. Values near the corners are always lower than values toward the center of each edge.

In all cases, the basic unit of measure is the meter. For clarity, the smallest ruled divisions of each scale vary in size. In general practice, and with adequate care, the level of precision approaches the limits of visual resolution, for any map, as shown in the following chart.

7. If your UTM coordinate counter gets dirty, it can be cleaned by rubbing it gently with a soft, nonabrasive artist's eraser, for example, the Vitagum Dry-Cleaner. Putty-like erasers are not as effective because they pick up skin oils and dirt. Abrasive erasers will scrape the printing from the surface of the counter.

8. Notice the format of the UTM Worksheet (see figure 4). It is an aid to taking notes while measuring UTM references. For a complete UTM grid reference for any point, there are spaces to be filled in for the zone number, easting value, and northing value. The position of each digit is clearly marked. The heavily underlined portions of the easting and northing values are read from the coordinate counter. All other digits may be read directly from the map.

9. One of the most frequent errors in writing UTM references is to reverse the easting and northing figures, with digits dropped or zeroes improperly added to make up for the different number of digits required for each. The correct formulation is easy to remember: a) Eastings are distances east (6 digits); b) Northings are distances north (7 digits); c) The order for writing UTM references is Z-E-N, zone-easting-northing.

10. Cheap straightedges, especially the common school and office rulers made of wood with brass edges, are notorious for drawing crooked lines. Even small deviations have a drastic effect on the accuracy of measurements.

To check the trueness of any straightedge, draw a long line with it, using a very sharp pencil. Turn the straightedge end for end, and draw another line connecting the ends of the first line. If the second line does not fall precisely along the first line for its entire length, then the straightedge is not straight.

The best source for reliable straightedges is an art or drafting supply store. College bookstores at schools where engineering, architecture, or drafting are taught are also good sources. The dealer should not object to you testing the edge.

11. For sites mapped with more than one point:
a) Begin with the northeasternmost point and proceed clockwise. If coordinates are written consistently in this way, computerizing UTM data will be much simpler. For example, as shown in figure 5a, list the points in alphabetical order, beginning with point A. (See also UTM Representation of Extensive and Complicated Sites.)
b) The simplest way to find the northeasternmost point of a figure is to line the map up with a T-square along the map border, and to pass a 45' line (NW-to SE) across the figure from the west to east. The last point it crosses before passing beyond the figure will be the northeasternmost point. A: 45' draftsman's triangle, or an adjustable triangle set at 45', moved along the T-square will show this line.
c) Some sites may have no point that is clearly farther northeast than the others. This will happen when a line connecting two or more corner points lies in the direction NW-to-SE; that is, 45' north of west. As in figure 5b, where neither of the points A or B is north east of the other, start with the northernmost of the two, A.
d) It is a good idea to label the points, both on the map and anywhere you write the references, to avoid confusion.

UTM Representation of Extensive and Complicated Sites

The goal of a UTM description is limited to fixing the location of a site in its geographical context and to conveying a reasonable impression of the site's shape and extent. Although it is an approximation, the UTM description should not be so loosely expressed that it could mislead a user by misrepresenting the site.

The UTM references for an extensive or complicated site have often been derived from the corner points of a rectangle drawn around the site (see figure 6a). While this approach fixes the site unambiguously on the map, and proves expedient for the mapper, it often falls short of the goal by seriously misrepresenting the shape and area of the site. The seriousness of this misrepresentation depends on how the data is to be used and on how much supporting information is available to guide a user's interpretation.

The general solution to the problem is to approximate such a site's boundaries by enclosing the site within a figure of more than four sides, or within a group of figures. As more points are plotted, less extraneous land is included. Figure 6b shows how the approximation of figure 6a could be improved by using more than four corner points, thereby reducing the extraneous (shaded) area. The mapper must reach a compromise between accuracy of representation and available working time, keeping in mind how the resulting information may be interpreted.

Extensive and complicated sites may be considered in four categories: complex, unclosed, discontinuous, and compound sites. Suggestions follow for choosing boundary points in each category.

Complex Sites

Complex sites have at least one border that does not conform to a side of a rectangle drawn on a USGS quadrangle map. They may be best represented by polygons of more than four sides (see figure 6b). UTM references for complex sites should be listed in National Register nomination forms beginning with the northeastern most point and continuing clockwise.

Unclosed Sites

An unclosed site does not form a closed geometric figure. If the site is small or if it follows a single straight line, a rectangle enclosing all points of the site may be an appropriate representation. However, if the site is extensive or if its boundaries curve or follow an irregular course, some other closed figure surrounding the site and conforming to its shape would be more appropriate (see figure 6c).

In some cases it may be possible to give an adequate representation of the site by a series of points connected by straight line segments, where the points are close enough to follow the curves (see figure 6d) but do not form a closed figure. As in representing complex sites, accuracy must be balanced against the amount of work required to record the site. Note: When the method chosen does not form a closed figure, the phrase "unclosed figure" should be written clearly on the nomination form beside the UTM references, and the references should be placed on the form in sequence from the northeasternmost end of the figure to the other end (A through E in figure 6d).

The common method of enclosing the meandering site in a series of rectangular boxes is no longer recommended. Although the results are similar to those in figure 6c, the method requires that many more corner points be drawn and measured.

Discontinuous Sites

A discontinuous site is composed of two or more separate features. Although the features of the site could be approximated by a single, closed figure (see figure 6e), the sense of the site would be distorted, implying that the area between the individual features is included. A better approach would be to plot a series of unconnected points or figures for each feature (see figure 6f), clearly labeling which points belong to each feature.

Compound Sites

A compound site is a discontinuous site with at least one feature described by multiple points, for example, two landing sites connected by a portage trail. Compound sites may be best represented by describing each feature separately. As shown in figure 6g, feature I is represented by points A-B-C; feature 2 by points D-E-F-G-H, feature 3 by points I+K-L. Features 1 and 3 are closed figures, but feature 2 is unclosed.

Method I

For each point to be measured, follow these steps, which will be easier to understand with map and tools at hand:
  1. Draw a line from the top of the map to the bottom, connecting the nearest equal-valued pair of UTM ticks to its west, that is, with the highest easting value west of the point.
  2. Draw a line from the left side to the right side of the map, connecting the nearest equal-valued pair of grid ticks to its south, that is, with the highest northing value south of the point. This will intersect the previous line somewhere to the south west of the point.
Note: If the point is so close to a map edge that either of these lines cannot be drawn, use Method IV.
  3. Remember that the UTM grid lines are generally not parallel to the map edges.
  4. Copy the zone number onto the worksheet.
  5. Copy onto the worksheet the printed portions of the easting and northing values appropriate to the UTM ticks through which the lines have been drawn. Not all ticks are labeled. It may be necessary to count from a nearby tick. Remember that (4) 77 is an abbreviation for 477,000 meters, that easting values increase going east, and that northing values increase going north. Check the distance between UTM ticks with the map scale before counting.
  6. Locate the scale on the coordinate counter matching the scale of the map. If no coordinate counter scale matches the map, use Method III.
  Align the counter on the map so that:
    a) the side of the scale that reads from right to left lies along the east-west line, and
    b) the side of the scale that reads from left to right passes through the point being measured (see figure 7).
  7. Read the coordinate counter scales, right-to-left for the easting and upward for the northing. Enter the measured values onto the worksheet (see figure 8).
  8. Check the readings for plausibility. Are all figures in the correct decimal places: does the easting have six digits and the northing seven? Do points directly east or west of one another have nearly equal northings? Do points directly north and south of one another have nearly equal eastings? Can you account for the differences?
  9. Check the figures for accuracy by remeasuring at least once.
  10. Be sure that the correct order is observed: zone, easting, northing.

Method II

For each point to be measured, follow these steps:
  1. Align the map to the T-square or parallel rule, with any two UTM ticks of equal value along the eastern and western map margins.
  Note: This may not make the map's own neat lines (edges of printing) square with the T-square. Alignment with the neat lines will inevitably create errors. This step is the key to accuracy in all further steps, so check the alignment carefully. Folds or curls in the map will make alignment difficult. It is advisable to relax a folded or curled map between flat, weighted surfaces for a day or so before measuring coordinates.

  Fasten down the map corners with masking or draftsman's tape, so that the map lies flat and smooth. The best way to tape down a map is shown in figure 9. Re-check alignment to be sure the map has not moved.

  To check alignment, draw a very fine line through a UTM tick on one side of the map, using the T-square. If the line passes exactly through the tick of equal value on the opposite side of the map, then the map is properly aligned.

  2. Draw a horizontal line along the T-square through the point to be measured, extending through the left or right edge of the map, whichever is closer.
  3. Using the T-square and triangle, draw a vertical line through the point, extending through the top or bottom edge of the map, whichever is closer.
  4. Remember to label each point and both of its projections (the points at which the lines in steps 2 and 3 cross the map edges).
  5. For each point to be measured, copy the zone number from the map onto the worksheet.
  6. Copy onto the worksheet the printed portion of the easting value of the nearest blue UTM tick mark to the left, west of, the point's projection on the top or bottom map edge. If the value of the tick is not printed on the map, it can easily be found by counting from nearby ticks. Establish the distance between ticks by checking against the map scale.
  7. Using the proper corner of the coordinate counter, align the ends of the appropriate measuring scale with the tick marks to the left and right of the point's projection on the top or bottom map edge. Be sure that the values on the measuring scale increase from left to right. Read the distance from the tick on the left to the point's projection, and enter this figure in the heavily underlined portion of the easting space on the worksheet.
  8. Copy onto the worksheet the printed portion of the northing value of the blue UTM tick nearest below, south of, the point's projection on the left or right map edge. (See step 6 for values not printed on the map.)
  9. Using the same corner of the counter, place the zero point on the tick below the point's projection. Be sure that the values on the measuring scale increase going upward, north (see figure 10). Read the distance from the lower (southern) tick to the point's projection, and enter this figure in the heavily underlined portion of the northing space on the worksheet.
  10. Check the measurements and copied values of eastings and northings by carefully remeasuring at least once.

Method III

The first two versions require a straightedge and a measuring scale that divides its units of measure into 10ths. Generally, the most satisfactory type of measuring scale will be a triangular engineer's scale, such as the Dietzgen 21636. A metric engineer's scale will also work.

Note: Method III is geometrically similar to the method commonly used for deriving latitude and longitude values in the Geographic Coordinate System.

Version 1

This version is useful when no drafting table and T-square are available, and when only one point on a map must be measured. When a drafting table and T-square are available, or when several points must be measured on the same map, version 2 should be used. For each point to be measured, follow these steps:
    1. Locate the point on the map.
    2. Draw four UTM grid lines to form a complete grid square surrounding the point. Whether or not a T-square is used, the straightness of the lines drawn is crucial to this method.
    3. Choose a measuring scale, minimum 10 units long with 10 subdivisions per unit, on which 10 units is longer than the distance between UTM grid ticks.
    4. Align the measuring scale so that:
       a) the zero point is along the western grid line,
       b) the 10-unit point is on the eastern grid line, and
       c) the edge of the scale passes through the point to be measured.
      Adjust the alignment carefully-accuracy of measurement depends on precise alignment (see figure 11).
    5. Read the scale, and write the distance between zero and the point in units and 10ths on a piece of scrap paper.
    6. Repeat steps 4 and 5, but with the zero point on the northern grid line and the 10-unit point on the southern grid line.
    7. Determine the measuring scale units.

This will be true for both eastings and northings.
    8. Write the easting and northing values on a worksheet, placing the printed and measured digits in their proper places.

Version 2

This version requires a drafting table, T-square, and triangle, in addition to the measuring scale mentioned in version 1. Although the set-up of the map on the drafting board is critical and it takes longer than version 1, this version makes measurement of several points on the same map quicker and more accurately.
Follow these steps:
  1. Align the UTM grid ticks on the map with the T-square, as in Method II. Tape the map down securely (see figure 9), and check the alignment, adjusting it if necessary. In most cases the T-square will not be parallel to the map edges.
  2. Draw lines connecting grid ticks of equal value to construct a grid square around each point to be measured.
  3. Choose any measuring scale on which 10 units, each divided into 10ths, span a distance greater than the distance between ticks.  
 4. For each grid square, align the zero point of the scale with the western grid line, and the 10-unit point of the scale with the eastern grid line. Mark the points on these two lines, and connect them with a diagonal straight line. Note that this need not be done within, or even near, the grid square itself, but may be done wherever convenient between the lines.
  5. Similarly, draw a diagonal line 10 units long between the north and south grid lines, wherever convenient.
  6. Using the T-square and triangle, project the point to the diagonal line just drawn between the east and west grid lines. This is equivalent to projecting the point to the border of the map, as in Method II. Label the point and its projection on the diagonal line.
  7. Using the T-square, project the point to the diagonal line just drawn between the north and south grid lines. Label the projection on the diagonal line.
  8. Use the measuring scale to measure the distance from the western grid line, along the diagonal line from steps 4 and 6, to the point's projection on the diagonal line. Note the measurement on scrap paper.
  9. Use the measuring scale to measure the distance from the southern grid line along the diagonal line from steps 5 and 7, to the point's projection on the line. Note this measurement on scrap paper.
  10. Determine the measuring scale units, as in step 7 of version 1.
  11. Write the easting and northing values on a worksheet, placing the printed and measured digits in their proper places.

Method IV

In figure 12, the point to be measured is so close to the southwest corner of the map sheet that no UTM ticks are printed to the south or west of it. Draw lines connecting the nearest pair of UTM ticks to the north and east of the site. Using the coordinate counter, measure distances from these lines to the site. This involves turning the coordinate counter 180 degrees from its normal position (see figure 12).

In the figure, the site is about 680 meters west of the nearest grid line to the east, and about 850 meters south of the nearest grid line to the north. To obtain the easting and northing values, subtract the measured distances from the UTM values associated with the grid lines:

Comparable methods may be worked out for points near the western and southern neat lines. For some only one subtraction will be needed. Check the logic of each measurement carefully, remembering that easting values always increase to the east and northing values always increase to the north.

One could construct extended grid lines and measure from them without subtraction. However, drawing the extensions frequently introduces mechanical errors, which are reflected in the UTM values. In practice, Method IV seems to give better results, and is recommended.
Note: This method may be used at any map scale, if the correct measuring scale on the coordinate counter is used.

Method V

Tables with UTM references for corner points of USGS quadrangles are found in Department of Army Technical Manual TM 5-241-11, "Universal Transverse Mercator Grid Tables for Latitudes 0 degrees-80 degrees" (Washington DE: Headquarters, Department of the Army, 1959).
A. Set-up (two examples are given as figures 14-16)
  1. Find the zone number of each map corner point.
    a) By reference to other maps showing this information for the same area
    b) By calculation:
      1) Western Hemisphere.
        (a) Divide longitude of point by 6.
        (b) Drop the fraction if there is a remainder: that is, round the result downward. 1.65 becomes 1
        (c) Subtract result in (b) from 30 giving the zone number.
      2) Eastern Hemisphere
        (a) Divide longitude of point by 6.
        (b) If there is a remainder, raise result to the nearest whole number; that is, round upward. 1.35 becomes 2
        (c) Add result in (b) to 30 giving the zone number.
  2. Note the longitude of the central meridian (CM) for the zone (see figure 13).
  3. Note the latitude and longitude of the corner point.
  4. Calculate the angular difference between the longitude of the CM and the longitude of the point by subtracting the smaller from the larger. This gives reference figure AD (angular difference).
 

  2. Count along the neat line, using the coordinate counter, measuring, marketing, and labeling the values of the points at which ticks would have been printed. On the north and south neat lines find points with easting values, so that a line through them will pass near enough to the site to give an easting reading. In the east and west neat lines, find points with equal northing values, so that a line through them will pass near enough to the site to give a northing reading.
  3. There is a shortcut for counting off large distances, such as might be encountered for a site near the middle of a quadrangle. Carefully cut the map scale from a spare quadrangle map printed to the same scale as the map containing the point. Or, using the map scale, mark off a long distance such as 10,000 meters on the edge of a piece of paper or index card. Dividers may also be used. Use this to set off large distances along the neat line. This is a more accurate method than repeated small measurements with the coordinate counter.
  4. Using a pair of the newly drawn ticks with equal values, align the map and tape it down.
  5. Check and adjust the alignment, which is crucial in this method.
  6. Using equal-valued pairs of the new tick marks, draw grid lines as in Method I around each point to be measured.
  7. Continue from step 3 of Method 1.

Rounding and the Degree of Precision

In general, it is best to measure site locations to the finest degree of precision possible with a given map and measuring tool. It is inadvisable to round measurements to a coarser degree of precision because this destroys a certain amount of information.

On the ground, one can measure distances with as much precision as the eye can see. Measuring ground distances from their representations on maps, however, imposes limits on precision. Map scale is a factor, compressing ground distances into map lengths difficult to distinguish by eye: one meter on the ground equals 1/24 millimeter on a 1:24,000-scale map. There are also limits in the precision of printing, so that even if one could see the map equivalent of an on-the-ground meter, the fine details of lines and points may not be printed accurately enough on a map to give an exact measurement.

For these reasons and others, including an increasing tendency for human error at high levels of precision, the table shown in the discussion of the coordinate counter also suggests the practical limits of precision for interpretation of USGS quadrangle maps. It will usually be unproductive, and may be misleading, to attempt measurements more precise than those indicated by the table. These practical limits have the effect of forcing the user to round measurements off to 10-, 25-, 50-, or 100-meter precisions, depending on the quadrangle scale.

When dealing with measurements from source maps at a variety of scales, take into account the degree of precision of each source and its effect on the use of UTM information. For example, consider a hypothetical site as its UTM reference might be measured at several map scales:

If the site were plotted on a new map at a very distant scale, say 1:250,000, the differences between these measurements would not be visible. At a closer scale, the choice of source measurement would influence placement on the map. At 1:24,000 in an urban area, the point as measured from a 1:250,000 map might be a block or more out of place. At closer scales, the displacement from true position due to rounding would be even more noticeable. Automated measurement and plotting will not resolve the discrepancies. Automation may eliminate mistakes, but it cannot improve on the inherent imprecision of the source map, nor can it enhance the degree of precision of recorded information.

For maximum accuracy, be sure that source map measurements are at least as precise as maps to be plotted from the data. When multiple points derived from sources of different precision are plotted together, decide whether accurate placement is critical enough to warrant annotating the map to show the precision of each point. One method of annotation is to use a different map symbol for each degree of precision. For example, represent measurement B as 10-meter precision by a cross (+), D at 50-meter precision by a star (*), E at 100-meter precision by a point(.).

If a decision is made that all points in a survey file will be recorded at the precision of the least precise measurement in the file, the resulting UTM references may still give problems in interpretation. It might be decided, for example, that all sites in a survey will have UTM references measured to the nearest 100 meters, since some sites are shown on 1:250,000 scale quadrangles, on which 100 meters is the smallest distance readily resolved by eye. When plotting maps at the 1:250,000 scale, this will cause no problem: one would not be able to see the difference between on-the-ground measurements to the nearest meter and the same references rounded to the nearest 100 meters. If, however, a map of points measured at 100-meter precision were plotted at 1:24,000, all the points scattered through a group of 100-meter squares would be plotted only at the nearest corner points of the squares. The dislocation would be quite evident at 1:24,000. If the points represented corner points of an historic district, the mismatch of precision between measurements and plotting would seriously distort the shape of the plotted area, as in figure 18.

Results of UTM reference measurements made by a digitizer may also be misleading because of precision problems (see Digitizing). Most digitizers measure to the nearest 100th of an inch; some measure at even greater precision. These precisions may be translated by using the scale factor into the on-the-ground distances they represent. If the digitizer measures with greater precision than that with which the source map is printed, then the reference values reported at the digitizer's precision may be inaccurate beyond the limits of precision of the map. In other words, the limit of precision of a measurement is set by the map or measuring tool, whichever has the least (coarsest) precision.

Digitizing

  1. Operator secures a source document on the digitizer's surface, which resembles a drafting board. Depending on the system, the document may have to be precisely aligned with a pre-established set of axes.
  2. A pointer is placed over two or three points on the document whose coordinates are already known. The coordinate values of each known point are typed into the machinery. This sets the system to measure in the same units, and with the same origin and axes, as the source document.
  3. The operator moves the pointer to any other point(s) on the document and the coordinates are automatically measured and calculated, and then displayed by a printer or other device. They may also be recorded for further computer processing.
  4. Depending on the equipment being used and on how it has been programmed (digitizing systems contain small computers or are connected with larger ones), measured coordinates may be converted mathematically to other measurement schemes, or areas contained within closed figures may be computed.
Note: Even if a USGS map lacks UTM ticks, the UTM references of its corner points are generally known, and may be used as the set-up points for a digitizer. Then any other points on the same map may be measured directly and reliably, avoiding the difficult and error-prone Method V. Ideally, the operator could enter the corner points in any coordinate system and the equipment would convert them to UTM to set up the digitizer if necessary. Values for measured points would be output in any coordinate system. These conversions depend on the capacity of the computer associated with the digitizer, however, and may not be available with all equipment.

Digitizing systems have become extremely sophisticated and expensive; some have capabilities for automated storage and retrieval of data, and for plotting. Others are part of much larger computer graphics systems, whose capabilities far exceed the need for simple measurement. Because of variety of available systems and the rapid growth of technology, any detailed recommendations given here would quickly become outdated. In principle, however, for situations where manual measurement is a burden, managers should investigate large engineering, planning, and utility offices to see what systems exist and if arrangements could be made to use them.

Computerizing UTM Data

When dealing with large areas, or areas containing hundreds of sites, the management of inventory data is cumbersome. The amount of labor needed to locate, extract, and synthesize information from the survey files is overwhelming. Computerized data expedites the flow of information to planners in a form most likely to receive their consideration. For example, with properly automated location data, it is possible to search a state's inventory files for the sites within 100 meters of a proposed path. Verbal information about sites of concern can be printed in the order and format best suited to the planners' needs, and maps or map overlays can be plotted automatically to show spatial relationships between the highway, the site, and other environmental features. As planning proceeds, the impact of alternate proposals may be similarly studied.

Further possibilities occur in other fields. Studies have been undertaken to test the value of environmental information in predicting the locations of archeological sites. The statistical correlation of environmental data with accurate location and cultural data for known sites is the key to such studies. Because of the complexity of the methods used, computer processing is necessary.

The generalized data format that follows will record enough data to fix the location of any point unambiguously. It provides sufficient information for performing geographic searches, and for formatting data to drive an automated plotter. The format is based on the full, numerical form of UTM notation with significant digits to the nearest meter. It accounts for multipoint, complex, and discontinuous sites, and those whose recorded boundary points do not form closed figures. The abbreviated forms of notation (see Variant Forms) are not recommended for automation because they require translation before mathematical computations can be performed, and may be ambiguous over large areas that cross zone boundaries. The recommended format is:

The format is used once for each point recorded. The zone, easting, and northing subfields are the standard UTM reference information for a single point. Should a site contain multiple, separate features, such as a series of mileposts, the feature subfield may be used to give a unique label to each feature. All points describing the same feature would contain the same value in the feature subfield. If there are multiple points within the same feature, each is labeled in order, using the point subfield. The convention used here is to begin labeling with the northeasternmost point, and to proceed clockwise. For the feature and point subfields letters or numbers may be used but numbers are recommended. The Pen field indicates whether an automatic plotter's pen should be raised or left on the paper before moving from one point to the next. By this means distinctions may be made between site features. Any binary (two-value) code may be used.

Using this format, the UTM data for the compound site in figure 6g would be coded as three features: the first a closed figure with three points, the second an unclosed figure with five points, and the third a closed figure with four points.

The letter D stands for pen down, U for pen up. The feature number remains constant for all points in the same feature. The point number is unique for each point within a feature, but the series of point numbers may start anew for each feature. In this example z, e, and n symbolize whatever UTM values are measured for each point.

Not included in this format is an indicator to show whether a site feature forms a closed figure; that is, whether a plotter pen should connect the last point of a feature with the first. This may be done by repeating a figure's first point immediately after the last with a pen code indicating pen down on the next-to-last point. It may also be shown by a closure field for each feature, instructing the plotter pen to return to the beginning point of a feature before moving to the next feature. The choice of these or other methods should be made by a programmer.

Depending on local needs, the format shown may be varied and editorial rules may be imposed. As long as variations are used consistently within the same file and can be translated back into the general format, compatibility between inventories can be maintained. For example, the format calls for three digits to record feature numbers; in many cases it may be determined that only two digits are necessary. If data recorded with two digits were to be merged with data having three digits, a leading zero could be added by the computer in a simple pre-processing step. Similarly, if one inventory used I and 0 to indicate pen up and pen down, while another used U and D, one set of codes could easily be converted to the other for common use. Letters may be used instead of numbers to label features or points. If programming is more convenient with the pen field following the UTM field, this rearrangement will not defeat the format, since the data could easily be reformatted as necessary to put the fields in another order.

In searching files of UTM data, the UTM reference field would be examined by the computer to determine whether a point lies within the area in which the inquirer is interested. If a map overlay were to be plotted, the UTM reference would also supply the X-Y coordinate data needed to position the point properly in relation to the map and to other plotted points. The pen, feature, and point subfields would be used in plotting to distinguish between features and to keep points in order.

When maps or overlays are plotted, scale will influence clarity. If the plot is at a distant scale (shows a large area), the symbols designating nearby points may overlap. To prevent this, some users may wish to record a single, central point for each site regardless of the site's extent, in addition to the several individual points describing the site in greater detail. For each plotting problem it must then be decided whether the single-point or multipoint representation would be clearer. The central point may be tagged with X or another symbol in the pen field to distinguish it from boundary points, or boundary points may be relegated to a separate data category. In either case, if the central point is used, it must be present in the record for each site, even if the complete list of UTM points for a site consists of only a single point. In files where most sites are represented by single points, this will result in much redundant data.

Extended UTM Grids

Variant Forms of UTM Notation

Digitized measurements cannot be made directly in variant forms.

The variant forms make use of the anterior digits, the small, raised digits at the left end (most significant digits) of grid values printed next to tick marks. Anterior digits represent hundreds of thousands of meters. In the UTM reference 17(6) '32840 (42)73525, the (6) and (42) are anterior digits, representing 600,000 and 4,200,000 meters, respectively.
The simplest class of variant notation is based on rounding data to the 10-, 100-, 1,000-, or 10,000-meter degrees of precision. For example: 17 632842 4273518 (general form, to the nearest meter) may be reduced to: 17 6328 42735 (100-meter precision) by dropping the rightmost or least significant two digits of the easting and northing. This may cause problems in applying UTM data, as discussed in Rounding and the Degree of Precision.

Another variant prefixes the easting and northing with the quadrangle name, dropping the zone number and anterior digits. While this form somewhat simplifies locating a site on a particular map, it produces ambiguities because quadrangles at different scales may have identical names. It is also a difficult notation to automate if UTM data is to be used for the purpose listed above. It is useful for small, personal files and for local surveys. For example, the general form of UTM reference for the northwest corner of the Executive Office Building, Washington, DC located in the Washington West Quadrangle, is: 18 323120 4307260. This reduces to Washington West 23120 07260, according to this method.

References in this form are difficult to plot on maps other than the USGS quadrangles on which they are measured. The quadrangle name, substituting for anterior digits, gives no clue to placement on, say, a state highway map or a broader-scale USGS quadrangle.

A variant form based on military usage is popular in Europe and Canada, but has the disadvantage of requiring reference tables for conversion to and from the general form. Except in areas limited to a single 100-km square on the UTM grid, it cannot readily be used for automated searching or plotting. Each UTM zone is divided into strips running east and west, usually 8 degrees of latitude wide. The strips are identified by a single alphabetic digit, according to the chart in figure 20. Within each strip in a zone, the area is divided into 100-km squares, each identified by a two-digit alphabetic code. The code for a square is derived from the zone number and the anterior digits of the eastings and northings within the square, according to the following tables provided by Peter Stott.

Determination of 100-km Square Designations for the UTM Kilometer Grid System

Like the six-digit figure itself, the easting value must always precede the northing value; thus the 100-km square for the Delaware Aqueduct is designated by the two-letter combination WA.

Using this form, the two-letter code substitutes for the anterior digits, and the easting and northing values are run together. The complete UTM reference for Executive Office Building would be:
18S UU 2312007260
where 18S gives the zone number and strip letter, necessary because the 100-km square designations repeat in each strip (see figure 20). It is customary to abbreviate references even further in this form by rounding eastings and northings, so that the six-digit form, 18S UU 231072, represents three digits each for easting and northing measurements, or 100-meter precision.

While these variants offer certain advantages for small-scale recording projects, the full numerical form of UTM reference is recommended for general use. It requires only a map with tick marks, a straightedge, a sharp pencil, and a coordinate counter, and uses no external reference tables. Because the reference in general form must be measured before conversion to a variant form, it should be no more difficult for the user to record. References in general form may be plotted by hand or computer on any map with UTM ticks, since the reference is a complete measurement from an original point along established axes. It is suggested that the quadrangle name and scale be recorded, but separately from the UTM reference, which is independent of map and scale.

Table A: Easting Values

Table B: Northing Values

Other USGS Map Series

Orthophotoquads have the appearance of high-altitude photographs at the same scale (1:24,000) as topographic quadrangle maps in the 7.5-minute series. Published orthophotoquads are printed in black and white, with the UTM grid superimposed. Diazo prints of advance (pre-publication) copies are available for orthophotoquads in certain stages of preparation. Advance copies have ticks for UTM, latitude and longitude, and state plane coordinate systems along the edges. Because all ticks on advance copies are printed in black, use care in choosing the correct ticks for measurement.

Very few names or symbols of topographic features are shown on published orthophotoquads, none on advance copies. The photographic rendering of ground features on orthophotoquads may, however, make site location easier than it would be in areas where few natural or man-made landmarks are shown in topographic maps.

To find out what areas have orthophotoquad coverage, request a free copy of the latest edition of the map, "Status of Orthophotoquad Mapping," from one of the two USGS Branch of Distribution offices (see Sources). At present, USGS has no plans for orthophotoquad coverage of Alaska, American Samoa, Guam, Panama Canal Zone, Puerto Rico, or the Virgin Islands. Quarterly updates for each state, called advance material indexes, are available from the four USGS regional mapping centers, (see Sources). I Advance copies of orthophotoquads are available only at these centers. Orthophotoquads and new or revised topographic maps are also reported when they are published in New Publications of the Geological Survey, published monthly and available free from the Branch of Distribution office in Arlington, VA, (see Sources).

An orthophotomap can be thought of as a photographic image covering a standard 7.5-minute quadrangle area, enhanced with drawn-in and labeled map features like those found in the topographic map series. Unlike the orthophotoquads, the orthophotomaps are printed with artificially constructed color representing the ground character, often with surprisingly beautiful results. Orthophotomaps are printed with all of the standard ticks; UTM ticks are blue. Availability is shown on the order forms and state indexes to topographic maps, where the designation OM following a quadrangle name indicates an orthophotomap. State indexes to topographic maps, order forms, and orthophotomaps are all available from the Branch of Distribution offices. Orthophotomaps have been prepared only for limited areas of the country.

The National Register of Historic Places will accept orthophotoquads in either advance or published form, on which UTM references to a site have been measured, if accompanied by a USGS topographic map, if necessary, at a different scale, on which the site location has also been marked. The topographic map is needed to relate the site to map features by name. Orthophotomaps are acceptable without accompanying topographic maps.

According to USGS, all published maps, including topographic quadrangles, orthophotoquads, and orthophotomaps are available from the Branch of Distribution offices either by mail order or over-the-counter; they are also available in small quantities at certain over-the-counter sales offices. Prices from commercial distributors may be higher. Unpublished (advance) versions of topographic maps and orthophotoquads are priced as shown on the advance material indexes for each state, and are available only at the four mapping centers.

Sources   A. Branch of Distribution, US Geological Survey, 1200 S. Eads Street, Arlington, VA 22202 -for areas east of the Mississippi River, including Minnesota, Puerto Rico, and the Virgin Islands
  B. Branch of Distribution, US Geological Survey, Box 25286, Federal Center, Denver, CO 80225 -for areas west of the Mississippi River, including Alaska, Hawaii, Louisiana, Guam, and American Samoa
  C. Eastern Mapping Center, US Geological Survey, Reston, VA 22092 -Alabama, Connecticut, Delaware, District of Columbia, Florida, Georgia, Indiana, Kentucky, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, and West Virginia
  D. Mid-Continent Mapping Center, US Geological Survey, Box 133, Rolla, MO 65401 -Arkansas, Illinois, Iowa, Kansas, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Nebraska, North Dakota, Oklahoma, South Dakota, and Wisconsin
  E. Rocky Mountain Mapping Center, US Geological Survey, Federal Center, Denver, CO 80225 -Alaska, Colorado, Montana, New Mexico, Texas, Utah and Wyoming
  F. Western Mapping Center, US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 -Arizona, California, Hawaii, Idaho, Nevada, Oregon, and Washington

(1)The reverse side of each advance material index shows what new advance and published topographic quadrangle maps have become available in the most recent quarter. Several advance stages of unpublished topographic maps may be available many months before published versions go on sale. A free nationwide index map, "Topographic Mapping: Status and Progress of Operations, 7.5-and 15minute series," is available free from Branch of Distribution offices.

Vocabulary

Figures, Graphs, Charts, etc.

(page numbers refer to the page in the printed version of this bulletin)

Page 26 - Figure 1. UTM Coordinate Counter
Page 27 - Figure 2. UTM Zones in the contiguous USA, Figure 3. A UTM zone
Page 28 - Figure 4. UTM Worksheet
Page 29 - Figure 5. Labeling Points clockwise from northeasternmost point, Figure 6. Problem Sites
Page 30 - Figure 7. Coordinate Counter set at the Wisconsin Historical Society
Page 31 - Figure 8. UTM Worksheet with two references from Madison, WI.
Page 32 - Figure 9. Securing map to drafting table
Page 33 - Figure 10. Measuring northing of Old Spring Tavern WI
Page 34 - Figure 11. Dividing the space between two grid lines
Page 35 - Figure 12. Measuring UTM reference near SW corner of map
Page 36 - Figure 13. Central Meridians for UTM zones, Figure 14. Method V
Page 37 - Figure 15. UTM Reference Table for corner point in Fig. 14
Page 38 - Figure 16. Method V, Figure 17. UTM Reference table for corner point in Fig. 16
Page 39 - continuation of Figure 17
Page 40 - Figure 18. Effects of rounding and degree of precision, Figure 19. Zone 18 Extended into Zone 17
Page 41 - Figure 20. UTM Military grid reference system zone and strip chart
Page 42 - Source of Figures