Cibola
Search and Rescue

Orienteering - Part 1

by John Mindock

This series of mini-lessons will focus on orienteering - the skills associated with map and compass. The goal of the series is to detail the aspects that are required to accurately use map/compass in the field. In addition, the student will be informed of common terminology associated with orienteering.

Many books have been written about orienteering - this series cannot cover every facet of the subject. The emphasis will be on those aspects that SAR personnel would most likely utilize on missions.

Finally, there is no substitute for field work. The best usage for this series is to attempt to comprehend the subject matter, then perform the suggested field exercises.

This first lesson describes salient features of topographical maps.

Topographical Maps

The word 'topography' refers to the 'layout' of the land ( hills, valleys, cliffs, etc.). A topographical map (topo, for short) depicts those aspects of the land's surface by using contour lines, colors, and other devices. The common topo is known as a 7.5 minute map, because it depicts 7.5 minutes of latitude and 7.5 minutes of longitude. The scale on a 7.5 minute map is 1:24000, roughly equating to 0.1 miles of terrain per 1/4 inch on the map. Another name used often is a 'quad', referring to the quadrangular shape of the map. Topos are named after a significant feature which they encompass (I.e., the Sandia Crest quad).

Most topos were developed in the 1950 - 1960 timeframe, and revised in the mid-1970's. This often results in mis-representation of current features.

Contour Lines

Picture a set of imaginary flat horizontal surfaces ('planes') that are parallel to one another, twenty feet apart, and slicing through the land. The contour lines shown on the topo are the intersection of the land with any of those planes, so that the outlines scribed by the lines provide a bird's-eye representation of the terrain.

The distance between adjacent contour lines is called the contour interval. Some maps use forty-foot contour intervals, while others use twenty. There is a phrase on the bottom margin of the map which states 'contour interval xx feet'. For the remainder of this series, we'll assume a contour interval of twenty feet.

If an area has many contour lines, the land rises upward more steeply compared to a place where there are few. With practice on a topo, one can become accomplished at envisioning the type of terrain depicted, recognizing features such as cliffs, ridges, valleys, arroyos, and saddles.

Colors

Typical Land Features

Contour lines for typical land features appear as follows:

Grids

Grids are man-made schema devised to provide reference lines/points for map features. The most interesting to SAR is the UTM (Universal Transverse Mercator). For this document, suffice it to say that UTM's are a set of numbers representing meters from the equator and meters from one of a group of 'North/South' lines. Although Latitude and Longitude are depicted on the map, their scale is usually too large for field personnel to use accurately.

Exercises - Orienteering Part 1

  1. Why are topos also called 7.5 minute maps?
  2. About how far (on land) is a distance represented by 3.75 inches on a topo?
  3. What are two differentials in altitude that contour lines often represent?
  4. How can one recognize steep areas by looking at a topo?
  5. What features are represented by the various colors on the topo?

Field Exercise

Go to a valley for which you have a topo. Locate nearby peaks, hills, saddles, etc. and compare what you see to the contour lines on the map. Then go to a high point and notice the appearance of the same features from the new perspective. Back to the Minilesson Page
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