l>Understanding Topographic Maps

Understanding Topographic Maps A topographic map, just put, is a two-dimensional representation of a portion of the three-dimensional surface ar of the earth. Topography is the form of the floor surface, and also topographic maps exist to represent the floor surface. Topographic maps room tools provided in geologic studies due to the fact that they present the configuration of the earth’s surface. Cartographers deal with the difficulty of representing the three-dimensional land surface ar on a level piece of paper by making use of contour lines, for this reason horizontal distances and vertical elevations can both be measured native a topographic map. Basic Information
The terms listed below indicate what details is contained on a topographic map, and where it can be found.

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

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

Contour Lines: edge lines are supplied to determine elevations and also are lines on a map that are produced from connecting point out of same elevation (elevation ad to elevation in feet, or meters, over sea level).

The adhering to are general qualities of contour lines:

1. Contour lines do not cross every other, divide or split. 2. Very closely spaced contour lines represent steep slopes, conversely, contour lines that room spaced far apart represent gentle slopes. 3. Edge lines tendency up valleys and form a "V" or a "U" whereby they cross a stream.

On many topographic maps, index contour lines are generally darker and also are significant with their elevations. Lighter contour lines carry out not have actually elevations, yet can be determined by counting increase or under from the nearest table of contents contour line and multiplying through the contour interval. The contour interval is stated on every topographic map and also is normally located listed below the scale.

Creating topographic profiles: Remember that topographic maps stand for a check out of the landscape as checked out from above. For producing a thorough study the a landform the is essential to build a topographic file or cross-section through a certain interval. A topographic profile is a cross-sectional see along a line attracted through a part of a topographic map.

A profile may be created quickly and also accurately across any right line ~ above a map by following this procedure:

a. Place a piece of file along a line throughout the area wherein the file is to it is in constructed.

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b. Mark on the record the specific place whereby each contour, stream and also hill peak crosses the profile line. c. Brand each mark with the elevation of the edge it represents. d. Prepare a vertical range on profile file by labeling the horizontal lines corresponding to the key of each index edge line. e. Location the record with the labeled contour lines at the bottom of the profile file and job each edge to the horizontal heat of the very same elevation. f. Attach the points.

Stream Gradient: Stream gradient can likewise be identified from a topographic map. The gradient that a heavy steam or flow is established by measure up a section of a currently or river and also dividing the street (in miles) into the vertical difference (in feet) between the 2 points. The result is to express in feet every mile (ft./mi.). The equation supplied is:

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

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Determining hillslope: among other things, a topographic map deserve to be used to measure up the typical slope the a hill (or hills).

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Topographic Map instance As an example, look in ~ a map of the Sulphur-Boundary Creek area along the middle Fork of the Salmon river This map is a geologic map the glacial geology in the area, attracted on a topographic map base. The map has a edge interval of forty feet, which way that every place between the marked 6800 foot line and the following lowest heat (which is 6760 feet, and also not marked) has an elevation same or higher than 6760 feet, but less 보다 6800 feet. You can figure out the elevation of any suggest by recognize the nearest labeled line, counting the variety of lines over or below it, multiplying by the edge interval, and including or subtracting the result from the nearest marked contour line. The more closely spaced the contour lines, the steeper the slope. You can find out precisely how steep the steep of the area you room interested in by individually the lowest elevation from the highest, and also dividing the result by the horizontal distance. Horizontal street is uncovered on the scale. Together you look at the map, notice that the contour lines enclose smaller and smaller areas. The smallest circles stand for the tops of peaks, and also some are marked with x’s v numbers alongside them. The numbers are the elevation at the peak of the peak.

follow a edge line follow me its length. Notification the indentations. As the edge lines cross gullies or present drainages, castle "vee" uphill. Drainages that have water in castle year-round have actually solid lines connecting the points of the vees. Drainages that have actually water only part of the year are marked with dashed lines.