l>Understanding Topographic Maps

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Understanding Topographic Maps A topographic map, merely put, is a two-dimensional depiction of a portion of the three-dimensional surface of the earth. Topography is the shape of the floor surface, and also topographic maps exist to stand for the soil surface. Topographic maps room tools provided in geologic studies since they show the construction of the earth’s surface. Cartographers resolve the difficulty of representing the three-dimensional land surface ar on a level piece of file by using contour lines, thus horizontal distances and also vertical elevations can both it is in measured native a topographic map. General Information
The terms listed below indicate what information is had on a topographic map, and where it have the right to be found.

Map Scale: Maps come in a selection of scales, covering locations ranging native the entire planet to a city block (or less).

Vertical range (contour interval): every maps have actually a horizontal scale. Topographic maps additionally have a vertical range to permit the determination of a suggest in 3 dimensional space.

Contour Lines: contour lines are used to recognize elevations and also are lines on a map the are created from connecting points of equal elevation (elevation advert to height in feet, or meters, above sea level).

The complying with are general qualities of contour lines:

1. Edge lines execute not cross each other, division or split. 2. Very closely spaced edge lines represent steep slopes, conversely, contour lines that room spaced far apart represent gentle slopes. 3. Edge lines trend up valleys and form a "V" or a "U" where they overcome a stream.

On many topographic maps, table of contents contour lines are typically darker and also are marked with their elevations. Lighter contour lines carry out not have elevations, however can be established by counting increase or under from the nearest table of contents contour line and also multiplying by the contour interval. The contour interval is stated on every topographic map and is typically located below the scale.

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Creating topographic profiles: Remember the topographic maps stand for a check out of the landscape as checked out from above. For developing a detailed study of a landform that is essential to construct a topographic profile or cross-section v a particular interval. A topographic file is a cross-sectional watch along a line drawn through a section of a topographic map.

A profile may be constructed quickly and also accurately across any right line top top a map by following this procedure:

a. Lay a piece of paper along a line across the area wherein the profile is to be constructed.

You are watching: On topographic maps contour lines that are farther apart indicate

b. Note on the file the exact place wherein each contour, stream and also hill height crosses the profile line. c. Brand each note with the key of the contour it represents. d. Prepare a vertical scale on profile file by labeling the horizontal lines corresponding to the key of each index edge line. e. Place the paper with the labeled contour lines in ~ the bottom of the profile record and project each edge to the horizontal heat of the exact same elevation. f. Affix the points.

Stream Gradient: Stream gradient can likewise be determined from a topographic map. The gradient the a heavy steam or flow is figured out by measure up a section of a present or river and dividing the distance (in miles) into the vertical distinction (in feet) between the 2 points. The an outcome is expressed in feet every mile (ft./mi.). The equation supplied is:


Tips for Interpreting Topographic Maps upright exaggeration: vertical exaggeration is the impact that is produced when the horizontal and also vertical scales on her topographic profile room not the same.

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Determining hillslope: amongst other things, a topographic map have the right to be supplied to measure the median slope of a hill (or hills).

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Topographic Map example As one example, look in ~ a map that the Sulphur-Boundary Creek area follow me the middle Fork the the Salmon flow This map is a geologic map of glacial geology in the area, drawn on a topographic map base. The map has actually a edge interval of fourty feet, which way that every place between the significant 6800 foot line and the following lowest heat (which is 6760 feet, and not marked) has actually an elevation equal or higher than 6760 feet, however less 보다 6800 feet. You can number out the elevation of any suggest by finding the nearest labeled line, counting the variety of lines over or below it, multiply by the contour interval, and including or individually the result from the nearest marked contour line. The an ext closely spaced the contour lines, the steeper the slope. Friend can uncover out specifically how steep the steep of the area you are interested in by subtracting the shortest elevation indigenous the highest, and dividing the result by the horizontal distance. Horizontal distance is discovered on the scale. Together you look in ~ the map, notice that the edge lines enclose smaller and also smaller areas. The smallest circles stand for the top of peaks, and some are marked with x’s with numbers next to them. The numbers room the key at the height of the peak.

follow a contour line along its length. Notification the indentations. As the edge lines overcome gullies or stream drainages, lock "vee" uphill. Drainages that have actually water in them year-round have solid lines connecting the points of the vees. Drainages that have water only part of the year are significant with dashed lines.