How to Read a Topographical Map - USDA

1 1 How to Read a Topographical MapA topographic map illustrates the topography, or the shape of theland, at the surface of the Earth. The topography is represented bycontour lines, which are imaginary lines. Every point on aparticular contour line is at the same elevation. These lines aregenerally relative to mean sea level. The illustration above on theright shows a correlation between the contour lines, and how thetopography of the land would appear from a horizon. Contour linesare generally illustrated as a brown to Read a Topographical MapIndividual contour lines on a Topographical map are a fixed intervalof elevation apart known as a contour interval. Common contourintervals are 5, 10, 20, 40, 80, or 100 feet. The actual contourinterval of a map depends upon the topography being representedas well as the scale of the map. If you look at the areas markedwith an orange box on this map you will see contour elevationnumbers.

2 This is the elevation of the contour line, relative to meansea to Read a Topographical MapContour lines that are relatively close together indicate a slope thatis fairly steep. Contour lines that are further apart indicates a slopethat is relatively flat. The area of the map above boxed in orangeshows an area that has a fairly steep slope, while the area boxed inpurple is a relatively flat to Read a Topographical MapContour lines on the map also show how water will travel acrossthe land. Contours that form a V can you tell which directionwater will flow. The bottom of the V points in the upstreamdirection. The orange line above shows the direction water wouldflow on this section of the to Read a Topographical MapOther features such as land cover, roadways, buildings andstructures, municipal boundaries, and water features are also shownon Topographical maps.

3 Water features such as streams, wetlands,rivers, drainage ditches, lakes, and ponds are usually illustrated asblue lines or blue colored to Read a Topographical MapLand use on a Topographical map is indicated by colors andsymbols. Wooded areas and other areas vegetated heavily withtrees and brush are green. Areas that have been cleared of trees,areas that are farmed, and open fields are white. Areas that areurbanized may be, green , white, or gray. Area 1 in the illustrationabove is wooded. Area 2 is a farm field. Area 3 contains housesand 3 Area 2 Area 17 How to Read a Topographical MapSymbols are used to indicate features on the map. For example,major highways are red lines, while other roads and streets areblack lines. House and buildings are usually black boxes,rectangles, or other geometric shapes. When reading atopographical map, try to utilize a map index that contains thesymbols commonly used on the maps.