 Engineers and land surveyors are the ones who generally measure and record the elevations using surveying equipment and tools for a variety of applications.

Grade measurements can be used for geographical features and landforms like hills, canyons, and river banks, and in residential, commercial, or industrial projects. They can be used in agriculture for irrigation, erecting retaining walls to stop soil erosion, landscaping to direct surface runoff away from building structures, construction to determine the roof pitch, etc.

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The slope or grade refers to the degree of inclination, change in the elevation of land over a distance. Simply put, it is the steepness between two specific points on an area of land.

How is it calculated?

We calculate terrain grade the same way the slope of a line is calculated. You need to have the coordinates of its endpoints. The slope is basically the quotient of the difference between the values of y and the difference between the values of x.

Formula:

slope = (y2 – y1) / (x2 – x1)

The change in the values of y is called the ‘rise,’ since it is along the vertical axis, while the difference in the values of x are known as the “run,” as it runs along the horizontal axis. This is how we get the popular equation of “slope is equal to rise overrun.”

Formula:

slope = rise/run

The grade can also be expressed in terms of angles using trigonometry. We need to obtain the angle between the horizontal plane and the plane of incline here.

The angle that goes up from the horizontal line is called the “angle of elevation,” and those that go down are called the “angle of declination.” This angle can be determined using the arctan function, which is the inverse of the tangent function with the slope as its article. You can use a trig calculator.

Formula:

Grade as an angle = arctan(rise/run)

Aside from determining grade using angles and ratios, we can also express it in percentage. Just multiply its ratio value to 100. A grade of one hundred percent means that the rise of the slope is equal to its run. So the resulting slope for this value is considered to be of average grade, neither steep nor flat.

Formula:

Grade in terms of percentage = (rise/run) * 100%

How can we understand elevation grade values?

Grade values are pretty simple for anyone to understand. A gentle slope has a terrain grade that is less than 1 (terrain grade <1); while a steep terrain is one that has a terrain grade greater than one (terrain grade >1).

If you want to know in terms of angle of elevation, then an angle above 45 degrees is considered a steep slope, while an angle below 45 degrees is considered relatively flat.