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location to determine the elevation at another location. As with
horizontal datums, the advanced technology of GPS has almost
completely replaced this classical technique of vertical measurement.
One of the main uses of the vertical datum is to measure rates of

subsidence, or land sinking.
By referencing the vertical datum, officials can determine the true
elevation and position of the hurricane evacuation routes, as well as

how much they have sunk over past decades.

Task 3. Answer the questions to the text.
1. What do geodesists and surveyors use datums for?

2. What is “datums”?
3. What is a local geodetic datum defined by?
4. What constants is the global geodetic datum defined by?

5. How do we define the horizontal datum?
6. How does the surveyor create a horizontal datum?
7. What is a vertical datum?
8. What do surveyors use to mark positions in the vertical datum?

9. What is the vertical datum used for?

Task 4. Define whether the following statements are true or
false and translate them. Correct the false ones according to
the text.

1. Datums are the basis for all geodetic survey work.

2. A local geodetic datum is used in satellite geodesy?
3. A global geodetic datum is defined by three constants to
specify the origin of the coordinate system (x, y, z).

4. To “connect” the horizontal monument into a unified network,
surveyors have used differential leveling.
5. Horizontal datum is used in monitoring the movement of the
Earth’s crust.

6. Triangulation uses a known elevation at one location to
determine the elevation at another location.
7. The vertical datum is used to measure rates of subsidence or

land sinking.

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