Map Reading and Navigation Flashcards

On a standard United States Geological Survey (USGS) 1:24,000 scale topographic map, approximately how many feet on the ground does one inch on the map represent?

Answer: 2,000 feet

A map scale of 1:24,000 means 1 unit on the map equals 24,000 of the same unit on the ground. Therefore, 1 inch on the map represents 24,000 inches on the ground. To convert this to feet, divide by 12 (since there are 12 inches in a foot): 24,000 / 12 = 2,000 feet.

A trooper is tasked with setting up a containment perimeter for a suspect last seen near an urban intersection. When using a standard city street map, what is the most critical initial step to ensure all potential vehicle escape routes are identified?

Answer: Identifying all major intersections, cross-streets, and alleys within the target radius.

To establish an effective perimeter, the primary goal is to block all avenues of escape. This requires a thorough examination of the map to identify every possible path a vehicle could take away from the location, including major roads, smaller side streets, and alleys, before units can be positioned effectively.

On a topographic map, what do closely spaced contour lines indicate?

Answer: A steep slope.

Contour lines connect points of equal elevation. When these lines are very close together, it signifies that the elevation is changing rapidly over a short horizontal distance, which represents a steep slope. Widely spaced lines indicate gentle slopes or flat terrain.

A trooper uses a GPS receiver set to the WGS 84 datum to find a specific coordinate. However, the physical topographic map being used for the operation is an older map printed using the NAD 27 datum. If this discrepancy is not accounted for, what is the most likely outcome?

Answer: The plotted GPS coordinate will be inaccurate on the map, potentially by a significant distance.

A map datum is a reference system for plotting locations. Different datums like WGS 84 (used by GPS) and NAD 27 use different models of the Earth. Plotting a coordinate from one system onto a map using another without conversion will result in a positional error that can be tens or even hundreds of meters, leading to a significant navigational mistake.

Which of the following best describes the reason a trooper must account for magnetic declination when navigating with a map and compass?

Answer: To correct the difference between magnetic north (where the compass points) and true north (the geographic North Pole shown on the map).

Maps are oriented to True North (the geographic North Pole), while a compass needle points to Magnetic North. Magnetic declination is the angle between these two norths for any given location. A trooper must adjust their compass bearing to account for this difference to accurately translate a direction from the map to the real world, or vice-versa.

A State Trooper is part of a search and rescue team in a large, rural state park. The command post provides coordinates in the Universal Transverse Mercator (UTM) system. What is the primary advantage of using UTM for this type of ground-level operation?

Answer: It provides a consistent grid system based on meters, which simplifies distance measurement and area calculation.

The UTM system overlays a square grid on the map, with distances measured in meters. This is highly advantageous for ground navigation because it allows for simple, consistent calculation of straight-line distances and the easy definition of search areas (e.g., a 500 by 500-meter grid). This is more straightforward than calculating distances with the angular units of latitude and longitude.