Maps

and a host of other issues - all best resolved through maps. You will have will learn later that the place to find maps is in the University Library, through government and commercial outlets and on-line from the Topo II , Topozone , TerraServer , or elsewhere - but how do you use maps? In teams of two, attempt as many of the following as time permits . You do not need to perform them in order, although some logically follow others (e.g., "relief" after "elevation")

Maps contain a wealth of information. The first and most important aspect of map interpretation is knowing what kind of map you are looking at. Examine the four maps given; what information can you gather from each map? Who might use this map? In a brief description of each map, list the information you can acquire from each map, the location and scale of the map and describe how you might use that information in the future.

NOTE: The following exercises refer to the Sedan, MT, 1:62,500 (1951) topographic quadrangle. Please do NOT write on the maps provided!

Location:

Location is determined with reference to one or more of the many grids [nearly rectangular or square coordinate systems] within which maps are defined.

The best-known is the (N-S) latitude-longitude (E-W) grid, which is familiar on world maps and globes. Most US maps are defined within that system, although they may include other systems.
- The corners of the quadrangle are labeled with their latitude and longitude. the units are degrees (°), minutes ('), and seconds (") of arc. What are the maximum and minimum latitude and longitude on this map? _________ _ long. to _________ _ long.; __________ _ lat. to __________ _ lat. [Note: longitude here is W est of the Prime Meridian at Greenwich, UK; latitude is N orth of the Equator.] What is the N-S extent of the map, in units of arc? ________ What is the E-W extent? _________ [that's why this is called the a "15-minute quadrangle.] Why isn't it square? _______________________________________________________________
- The map is divided by tics along the margins and four small pluses (+) within the map into nine segments, each ______ minutes of arc on a side. These are small enough to measure with a standard ruler.
  - Locate the segment in which Fairy Lake is located.
  - Measure the E-W distance, in cm, between the 5-minute tics to the N of Fairy Lake ______. That is the map-equivalent distance to 5 minutes, or 300 seconds, of arc. How many seconds of longitude are covered by 1 cm? _________ Is that number the same on all other maps at the same scale? _________
  - Measure the distance, in cm, by which Fairy Lake is E of the western map margin. _______ What is the equivalent in seconds of longitude? ________ That is the amount by which the longitude of Fairy Lake is less than 111° 00' 00"W. What would the longitude of Fairy Lake be in ° ' " W of Greenwich? ____________
  - Measure the N-S distance, in cm, between the 5-minute tics to the W of Fairy Lake ______. That is the map-equivalent distance to 5 minutes, or 300 seconds, of arc. How many seconds of latitude are covered by 1 cm? _________ Is that number the same on all other maps at the same scale? _________
  - Measure the distance, in cm, by which Fairy Lake is S of the 55' tic on western map margin. _______ What is the equivalent in seconds of latitude? ________ That is the amount by which the latitude of Fairy Lake is less than 45° 55' 00"N. What would the latitude of Fairy Lake be in ° ' " N of the Equator? ____________
The other major grid system is the Land Office, or " Township-Range " grid. The grid consists of Townships, six miles square, defined relative to a number of N-S Principal Meridians and E-W Baselines. Each township is labeled along the margins of the maps by their order N or S of their baseline, and by their range E or W of their prime meridian. The townships are outlined by heavy solid or dashed red lines.
- Townships are subdivided into sections, one mile "square". Those are labeled on the map. Notice the unusual order of numbering! Sections are subdivided into quarters (NE, NW, SE, NW), which can in turn be quartered, ad infinitum .
  - What is the location of Fairy Lake in the Land Office system? ___¼, ___¼, section ______, T____, R____.

Elevation

Elevations are determined on maps in either English units (feet) or metric units (meters). They are shown as labeled points (BM = bench mark) rounded to the nearest foot from accurate surveys; as spot elevations (x or nothing), accurate to ± 0.3 contour interval; or as interpolations from contour lines , accurate to ± 0.5 contour interval. Interpolation is generally to the nearest 1/2 contour interval (here, equal to what? _____).

Relief

Relief is simply the arithmetic difference (highest - lowest) between two points of interest. The uncertainty is the square root of the sum of the squared individual errors. Note that slope (rise/run) can be calculated from relief (rise) and distance (run).

Distance

Distance is measured using either the bar scale or the fractional scale . The bar scales are located at bottom center of the map, and are given in a number of units. The fractional scale is found above the bar scales, in the form of the ration between a distance on the map and the distance between the same points on the ground. What is the fractional scale of this map? ___:_____________

Straight-line distance is simply scaled directly from the map.
- What is the straight-line distance (in inches) between Fairy Lake and the Fairy Lake/Sedan road junction? _____ in
- From the bar scale, what is that distance (in feet)? ______ ft [Note that you can line the zero point of your ruler up on a 1000-ft tic and interpolate between 500-ft tics at the other end.]
- Now, multiply your measurement by 62,500 and divide by 12. [Note: use Start, Programs, Accessories, Calculator to bring up the Windows calculator. Use View to switch from standard to scientific as desired.] _________ ft.
Curved-line distance is a different story. perhaps the easiest way to measure a curvy line is to break it into a number of (nearly) straight segments, and add them together by rocking your ruler along the line as it bends. You can do the same thing with the edge of a piece of paper, making a very light tic on map and paper at each corner to help line up the next straight. Then - measure the length of the edge of the paper!
- What is the road distance from the above road junction to Fairy Lake? __________ ft [Note: it can be a real nice ski or snowmobile trip after a fresh snow!]

Direction

Direction is measured with a protractor relative to True North or Magnetic North according to the declination diagram in the lower map margin. "Relative to" means in degrees E or W of North (or South), or as an azimuth (out of 360°, where N is 0°, E is 90°, S is 180°, and W is 270°).Why do you need more than one North, anyway? ____________________________________________________________________________________________________________

Contouring

Contours are lines connecting equal values. Many data types other than elevation are shown by contoured maps - ground-water levels, geochemical characteristics, and rainfall amounts, to name a few. How do they do that? By following a few simple rules (some of which have rare exceptions).

Rule	Exception
Contour numbering starts at zero
Contours are equally spaced - the "contour interval"	Supplemental (dashed) lines may be inserted for detail
Every fifth line is a master contour ( heavy line )
Contours must close on themselves	Lines "end" at the edge of a map
Contours never join, split, or cross	Lines may merge and diverge at a vertical cliff
Contour numbers repeat across a high or low spot
Between known points the slope is assumed constant
Contours are usually smooth, but "V" up a stream	Ridges may "V" downhill as well

Apply the rules above to contour the data points you are given. When you are done, compare your results to the topographic map of the Bozeman area . Can you recognize the source of the data?

NOTE: For a more in-depth discussion of topographic map interpretation, see the instructions for Geomorphology - ESCI 307.

As a group, discuss what you have learned. Have you heard of these concepts before - if so, in what context? In what contexts do you expect to hear about them
again? Have you used topographic maps before - when and where? What have you learned here that might help your future map use?