Overview
This lecture explains how to read topographic maps, focusing on contour lines, map scales, and the interpretation of symbols and colors.
Contour Lines
- Contour lines connect points of equal elevation on a map.
- Closely spaced contour lines indicate steep terrain; widely spaced lines mean gentle slopes.
- Concentric contour lines forming smaller circles often represent peaks.
- Every fifth contour line is an index line, which is thicker and labeled with its elevation.
- The contour interval is the vertical distance between adjacent contour lines, commonly 40 or 80 feet.
- Information about contour intervals and index lines can be found in the map legend.
Understanding Map Scale
- Scale shows the ratio of map distance to real-world distance (e.g., 1:12,000 means 1 inch = 12,000 inches in reality).
- A map with a smaller scale covers a larger area with less detail, while a larger scale covers a smaller area with more detail.
- Representative scales (like a bar scale) near the legend help measure distances easily using a compass edge or string.
Map Symbols, Colors, and Legend
- The legend explains the meaning of lines, colors, and symbols used on the map.
- Darker colors typically show denser vegetation; colors lighten near mountain peaks as forests thin out.
- Blue colors represent streams and lakes.
- The legend also includes information about contour lines, map revision dates, and the region’s magnetic declination (for compass use).
Key Terms & Definitions
- Contour Line — A line connecting points at the same elevation.
- Index Line — A thicker contour line labeled with its elevation, appearing every fifth line.
- Contour Interval — The vertical distance between two adjacent contour lines.
- Scale — The proportion of map distance to actual ground distance.
- Legend — The map’s guide explaining symbols, colors, and important information.
- Magnetic Declination — The angle difference between true north and magnetic north shown on the map.
Action Items / Next Steps
- Study a familiar area on a topographic map to practice interpreting contour lines.
- Review the map legend to familiarize yourself with its symbols and details.
- Prepare to learn how to use a compass with your map in upcoming lessons.