Topographic Maps: Contour Lines, Slope, and Map Scales

Topographic map

Projection of a three-dimensional surface onto a two-dimensional surface

Contour lines

Lines that connect points of equal elevation

Contour interval

Difference in elevation between adjacent contour lines (10 feet, 20 feet, etc.)

Index contour

Every fifth contour; has elevations printed on it

Slope

Lines close together = steep slope

Lines far apart = gentle/flat area

Rule of V's

The pointy end = upstream (higher elevation); The open end = downstream (lower elevation); Water always flows opposite the direction the V points

Map Scale

Ratio scale - 1:100,000 (unitless)

Fractional scale - 1/100,000 (unitless)

Verbal scale - 1 inch = 1000 feet

Map magnetic declination

Difference in degrees between true north and magnetic north

Grid north (Gn)

Located at top of quadrangle

Magnetic north (MN)

Direction a compass points

True north (TN)

Pole of the earth's axis of rotation

Latitude

North to south of the equator

Longitude

East to west of prime meridian

Relief calculation

Difference in elevation between two points

Gradient calculation

Given as a ratio or as a percent; Vertical distance (Rise) / Horizontal distance (Run)