Maps
Note: The following information is based on recommendations from the National Association for Search and Rescue's (NASAR) Fundamentals of Search and Rescue 2nd Edition handbook.
Learning Objectives
Upon completing this module, responders should be able to:
Topographic Features: Interpret contour lines to identify terrain landforms, elevation changes, and slope steepness on a USGS topographic map.
Map Scale & Distance: Calculate real-world ground distances using map scales, bar scales, and grid lines.
Coordinate Systems: Plot and read location coordinates using Latitude/Longitude, Universal Transverse Mercator (UTM), and the United States National Grid (USNG).
Declination & Orientation: Explain the difference between True North, Magnetic North, and Grid North, and apply magnetic declination corrections.
1. Topographic Map Fundamentals
Topographic maps are essential tools for search planning, land navigation, and grid assignments. Unlike standard road maps, they represent the three-dimensional shape of the earth's surface on a two-dimensional page.
Understanding Contour Lines
Contour Lines: Lines connecting points of equal elevation above sea level.
Index Contours: Heavier, darker lines printed with specific elevation numbers at regular intervals.
Contour Interval: The vertical distance in elevation between adjacent contour lines (found in the map legend).
Terrain Landforms:
Steep Terrain: Contour lines closely spaced together.
Gentle Slopes: Contour lines widely spaced apart.
Peaks & Knolls: Concentric closed loops.
Valleys & Draws: V-shaped contours pointing upstream toward higher elevation.
Ridges: V- or U-shaped contours pointing downstream toward lower elevation.
2. Scale & Distance Measurement
Map scale defines the mathematical relationship between distances measured on the map and actual ground distances in the field.
Map Scale Ratios
1:24,000 Scale (USGS 7.5-Minute Series): Standard for SAR land navigation. 1 inch on the map equals 24,000 inches (2,000 feet) on the ground.
1:50,000 Scale: Common for military operations; 1 cm on the map equals 500 meters on the ground.
Measuring Distance: Use a grid reader, ruler, or paper edge alongside the map’s graphic bar scale to measure straight-line distance, or use a flexible string to trace winding trails and streams.
3. Coordinate Reference Systems
Accurate communication of location coordinates between field teams and Incident Command prevents search errors and speeds up emergency rescues.
Primary Systems
Latitude & Longitude: Expressed in degrees, minutes, and seconds (° ' "). Latitude measures position north/south of the equator; Longitude measures position east/west of the Prime Meridian.
Universal Transverse Mercator (UTM): Divides the earth into a 60-zone grid using metric distances (Easting and Northing values in meters), making field distance calculations simpler than angular degrees.
United States National Grid (USNG): Built on the UTM system, USNG provides a seamless, standardized grid format used across emergency response agencies nationwide to eliminate location ambiguity.
4. North Baselines & Magnetic Declination
Navigating accurately requires understanding the three distinct definitions of "North" printed on topographic maps.
The Three Norths
True North (TN): The geographic North Pole where all lines of longitude converge.
Grid North (GN): The direction of the vertical grid lines printed on a map projection.
Magnetic North (MN): The direction a physical compass needle points, aligned with the earth's magnetic field (which fluctuates over time).
Managing Declination
Magnetic Declination: The angular difference between True North and Magnetic North for a specific geographic location.
Correction Rules: Responders must adjust their compass settings or calculations when transferring bearings between a map (True/Grid North) and a magnetic compass in the field (Magnetic North) using the diagram provided on the map's margin.
5. The U.S. Public Land Survey System (PLSS)
The Public Land Survey System (PLSS)—often referred to as the "Rectangular Survey System"—is the traditional method used to subdivide and describe land ownership across much of the United States. In SAR operations, local land descriptions, property boundaries, and dispatch calls frequently reference PLSS designations.
Grid Hierarchy
Township and Range: Land is surveyed into a grid anchored by a primary Principal Meridian (north-south line) and a Base Line (east-west line).
Townships (T): 6-mile-wide horizontal rows running north or south of the Base Line (e.g., T5N).
Ranges (R): 6-mile-wide vertical columns running east or west of the Principal Meridian (e.g., R3W).
Township Square: The 36-square-mile area formed by the intersection of a Township row and Range column.
Sections: Each 36-square-mile township square is divided into 36 Sections, each measuring 1 mile by 1 mile (640 acres). Sections are numbered sequentially in a "snake-like" pattern starting from Section 1 in the northeast corner to Section 36 in the southeast corner.
Subdivisions (Quarter-Sections): Sections are further divided into quarters (160 acres each)—Northeast (NE), Northwest (NW), Southeast (SE), and Southwest (SW)—and can be quartered again down to 40-acre tracts.
Reading a PLSS Legal Description: PLSS locations are read from smallest unit to largest unit (e.g., NE 1/4 of the SW 1/4, Section 14, T5N, R3W).
Useful Tools
These links will bring you to tools that will help you convert coordinate systems. For example, if you wanted to convert a latitude/longitude system to a UTM coordinate:
The USGS has many topographical maps available online.
This website provided by the FCC will let you know if you will be in the range of cellular coverage.