Contours at different elevations can't cross one another. Contour lines that are V-shaped and have convexity toward higher ground are signs of valleys.ġ5. Contour lines in U-shape that show convexity toward the ground mark the ridge.ġ4. Closed contours that are approximately concentric with higher values towards the middle indicate hills.ġ3. Closed contours that are concentric and with lower values towards the middle are indicative of a pond.ġ2. The same contours are required on both sides of a valley or a valley.ġ1. Irregular contours indicate uneven surfaces.ĩ. Any point of contour is parallel to the slope of the slope that is steepest at that point.Ĩ. A contour line should be able to close to the map, but does not have to be within the boundaries of the map.ħ. If you draw the contours parallel to each other, parallel, and straight these contours represent sloped plane surfaces.Ħ. Equally spaced contours show an even slope. Contours that lie close to each other show steep slopes, while contours that are drawn separately represent a gentle slope.ĥ. Contours with different elevations do not join to create a single contour, except for the vertical cliff.Ĥ. Two contours with different elevations do not meet, except when there is the cliff's overhang.ģ. The horizontal distance between two contour lines is a measure of the slope of the line and changes in inverse proportion to the slope.Ģ. The most important aspect of the contour could be summarized as in the following manner:ġ. The characteristics of Contour in Surveying Then divide 100 by 5 100/5 = 20 units A contour Interval on the previous map is 20 units. The total numbers of contour lines between 71 is 4. The difference between 71 value is 7100 + 700 = 100. The final result we get after division the contour interval from the topographic map that is specific to it.Īn Example of Calculation for Contour Intervals:īased on the above map and the steps to follow in calculating the contour interval is to take the following example: 71, and determine the interval in between. The last step is the ratio from the differences between two index lines (step 2) and the number of lines between the two index lines plus one (step five). For instance, if the lines that lie between two index lines is five. The line count obtained during the previous step is added and rounded to 1. Now, you can count the number non-index lines that contour lines are between the two contour lines used for the contour interval calculation in the initial step. To calculate this difference subtracting the upper elevated line from the reading of the lower elevated line. Then calculate what is the difference in the two index contour line from the map. The first step is to locate 2 index contour lines which are marked with a specific elevation. The method of calculating the contour intervals can be done as follows: In the above image the dark lines that have readings are contour lines that are indexes. The lines that are marked or labeled are called Index Contour Lines. To make the contour map easy to comprehend it is not necessary that every contour line is labeled with its elevation reading. How can I calculate Contour Interval using Maps?Ī contour map is made up of contour lines within an area of a particular geographical. The most commonly used range of contours is around 20 feet on the 1:24,000 scale map. If the contour range is not stated on the maps, it could be calculated using the methods described in the sections below. On every maps, in the right bottom the contour interval is indicated. When considering the size of the space to be mapped the contour intervals are considered. There are usually different contour intervals on various maps. A contour interval is the vertical distance or difference in elevation between two contour lines of the topographical map.
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