TOPOGRAPHY NOTES LOOKING AT YOUR MAP Where are

TOPOGRAPHY NOTES

LOOKING AT YOUR MAP Where are the steepest slopes? Where would be the best place to build a trail to climb to the top of the mountain?

LOOKING AT YOUR MAP: WHAT DO YOU THINK TOPOGRAPHY IS? Describe the topography of your map. Define topography. How many contour lines did you draw? Define contour line. How would you define a contour line? What is the vertical distance or contour line interval on your map? Topography is the shapes and features of the Earth’s surface. This type of map uses contour lines to show the shape and elevation of the land. A contour line is a line that connects places on a topographic map that are all at the same elevation. Elevation is the height above sea level. There are many contour lines on a topographic map. The vertical distance between neighboring contour lines is called the contour line interval. Contour interval is the actual change in elevation represented by the space between two adjacent topographic "rings". For example, if there is a contour interval of 20 feet, each topographic line on the map represents going either up or down by 20 feet of elevation. For convenience, many mapmakers include numbers every four or five lines to tell you what elevation is represented by that line.

WHY WOULD A TOPOGRAPHIC MAP NEED A SCALE? A topographic map has to have a scale and interval defined. A scale of 1: 24, 000, commonly used in USGS topographic maps, means that one unit on the map represents 24, 000 units on the ground. The units are commonly taken as being in inches rather than metric in the US. Therefore, one inch on the map represents 24, 000 inches on the ground, which is exactly 2, 000 feet, or 0. 38 miles. Most topographic maps are marked in feet, but may have a metric key at the bottom.

WHAT WOULD MAKE YOUR CONTOUR LINES STAND OUT BETTER? Color is important on a topographic map. The first features usually noticed on a topographic map are the colors. Brown, blue, and green are the most common in rural areas while brown, red, and black are found in urban areas.

HOW WOULD YOU TELL A STEEP SLOPE FROM LEVEL LAND? To help the user determine elevations, index contours are used. Index contours are a wider line. Elevation is printed in several places along these lines. The narrower contour lines found between the wider index contours help to show more details of the land surface shape. Contours that are very close together represent steep slopes. Widely spaced contours, or an absence of contours, means that the ground slope is relatively level. The contour interval is printed in the margin of each U. S. Geological Survey (USGS) map.

HOW DO YOU KNOW WHEN A CONTOUR LINE CROSSES A STREAM OR VALLEY? Where a contour line crosses a stream or valley, the contour line bends to form a ―V‖ that points upstream. In the upstream direction, the successive contours represent higher elevations. Contour lines near the top of a hill form closed, circular shapes. The top of the hill is higher than the highest closed contour line.

HOW DO YOU TELL THE DIFFERENCE BETWEEN A GENTLE SLOPE AND A STEEP SLOPE? Depressions without outlets are shown by closed hatched contours. The contour lines have short lines on the inside that are pointing downslope. The bottom of the depression is lower than the lowest closed contour line. Contour lines are widely spaced on gentle slopes. Contour lines are closely spaced on steep slopes.

Contour lines do not cross or intersect each other, except in the rare case of an overhanging cliff. All contour lines eventually will make a closed loop. This closure may be on the map or beyond its margins since contour lines connect features of the same elevation.