find the area of the whole land?
it's important
Answers
Answer:
One of the main purposes of your topographical survey may be to determine the area of a tract of land where you want to build a fish-farm. From existing topographical maps, you may need to calculate the area of a watershed or of a future reservoir (see Water, Volume 4 in this series).
Note: in land surveying, you should regard land areas as horizontal surfaces, not as the actual area of the ground surface. You always measure horizontal distances.
2. You will often need to know the areas of cross-section profiles to calculate the amount of earthwork you need to do.
Horizontal area
182.GIF (17886 byte)
Cross-section area
182a.GIF (22293 byte)
3. You may determine areas either directly from field measurements, or indirectly, from a plan or map. In the first case, you will find all the measurements of distances and angles you need by surveying, and you will calculate the areas from them. In the second case, you will draw a plan or map first (see Chapter 9). Then you will get the dimensions you need from the scale, and determine the area on that basis.
4. There are several simple methods available for measuring areas. Some of these are graphic methods, where you compare the plan or map of the area you need to measure to a drawn pattern of known unit sizes. Others are geometric methods, where you use simple mathematical formulas to calculate areas of regular geometrical figures, such as triangles, trapeziums*, or areas bounded by an irregular curve.
Note: a trapezium is a four-sided polygon with two parallel sides.
5. The simple methods will be described in detail in the next sections. They are also summarized in Table 13.
Triangle
183.GIF (1779 byte)
Trapezium 1
183a.GIF (2136 byte)
Trapezium 2
183b.GIF (1752 byte)
Irregular area
183c.GIF (2323 byte)
TABLE 13
Simple area measurement methods
Section
Method
Remarks
10.2 Strips Graphic method giving rough estimate
10.3 Square-grid Graphic method giving good to very good estimates
10.4 Subdivision into regular geometric figures such as, triangles, trapeziums Geometric method giving good to very good estimates
10.5 Trapezoidal rule Geometric method giving good to very good estimates Suitable for curved boundary
10.2 How to use the strips method for measuring areas
1. Get a piece of transparent paper, such as tracing paper or light-weight square-ruled millimetric paper. Its size will depend on the size of the mapped area you need to measure.
2. On this paper, draw a series of strips, by drawing a series of parallel lines at a regular, fixed interval. Choose this strip width W to represent a certain number of metres. You can follow the scale of the plan or map to do this.
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Answer:
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Step-by-step explanation:
Where is land?