Use the appropriate conversion factor to convert the horizontal map distance to horizontal ground distance. The desired unit is feet. Set up the cancellation table so all units will cancel, except the desired unit, feet. Step 4. Use the slope percent equation and solve. The run is feet and the rise in elevation is feet. Line 1 starts with the contour interval, not the projection point. Slope Worksheet to be completed. Skip to main content.
View Navigation. Topographic maps show contour lines for only certain elevations. These lines are evenly spaced apart. This spacing is called the contour interval. To make topographic maps easier to read, every fifth contour line is an index contour.
The index contour lines are the only ones labeled. The index contours are a darker or wider line in comparison to the regular contour lines. Elevations are marked on the index contour lines only. First step is to add a new field. Next, we can select those contours that are multiples of This is a small enough layer that if we really wanted to we could just do it manually by sorting our Contour values and only changing the ones we need to.
Now how can we efficiently use a query to pick out all the contours whose elevation value is a multiple of ? Those of you who have done any coding will likely have come across the modulo function. It depends on how steep the hill is; if it is a gentle slope you may have to walk a long time before you reach a higher elevation of 20ft. On a topographic map, the contour lines for this hill would be spaced far apart. Recall that a slope gradient is the change in elevation divided by the distance; you can easily calculate the slope of your hill or any region on a topographic map if you know the change in elevation between two points, and if you know the distance between those same two points.
Remember to use the contour lines to determine the elevations, and the bar scale on your map to measure the distance. In addition to contour lines, topographic maps will also have benchmarks actual surveyed points in various locations on your map. These surveyed points are exact elevations above sea level and are commonly used to mark the elevations of mountains, hilltops, road intersections, and airport runways. Benchmark locations will normally be found in the area between contour lines.
For example, a benchmark of ft will be found somewhere between the ft and ft contour line if the contour interval is 10ft , or between the ft and ft contour line if the contour interval is 5ft. In addition to obeying the set contour interval for a map, contour lines should never branch split or simply end inside of the mapped region.
Instead, these lines are continuous, although they can continue off the edge of the map. Contour lines also never touch or overlap, unless certain rare instances occur, such as if there is a vertical or overhanging cliff. In the case of a vertical cliff, the contour lines will appear to merge. The entire third dimension elevation represented by the contour lines on a topographic map is called the relief and is easily determined if you can find the highest and lowest contour line elevations and subtract the two values to determine the vertical relief represented in the map.
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