Lecture 5 23/01/2017 (Part A)

Question 1

What is UTM? What type of coordinate system is it?

Answer 1

1. Universal Transverse Mercator

2. A projected coordinate system

Question 2

What is georeferencing?

Answer 2

Georeferencing is:

1. Calibrating geographic coordinates
2. associated with an object in geographic space
3. relative to an established geographic referencing system such as a datum.

Question 3

What is a datum?

Answer 3

A datum is:

1. A network of benchmarks OR
2. starting points for interpolating distance and elevation values external to itself.
3. Values determined through use of a datum are
4. relative to a mathematical structure
5. which equates earths surface to the shape of an ellipsoid.
6. There are two types of datums:
7. vertical and horizontal, however,
8. in some cases these have been condensed into geometric datums.

Question 4

What are the two types of datums?

Answer 4

1. Horizontal; and

2. Vertical

Question 5

Datums are modelled through ________.

Answer 5

Geodesy

Question 6

What is Geodesy?

Answer 6

1. The branch of science which deals with
2. the size and shape of earth including:
3. physical geodesy - detailing the earth’s gravity field and
4. geometric geodesy - determining spatial relationships with coordinate systems.

Question 7

What is Geodesy based upon?

Answer 7

1. Geometric principles
2. Earth’s internal gravity field (geoid)
3. Earth’s rotation (ellipsoid)

Question 8

What determines the shape of earth?

Answer 8

Gravity

Question 9

What is the shape of the earth? In what dimension is it squished?

Answer 9

1. Ellipsoid

2. Y-axis (up and down)

Question 10

What is a geoid?

Answer 10

A Geoid is:

1. The equipotential surface of the Earth’s gravity field that
2. best fits global mean sea level;
3. vertical reference is determined by relative gravity.

Question 11

What is a Horizontal Datum? Provide an example.

Answer 11

A network of benchmarks identified by coordinates (e.g., North American Datum 1927 [NAD27], North American Datum 1983 [NAD83]).

Question 12

What is a Vertical Datum? Provide an example.

Answer 12

A network of spatially distributed points on the Earth with known heights either above or below sea level. (e.g., National Geodetic Vertical Datum 1929 [NGVD29] ,
National Geodetic Vertical Datum 1988 [NGVD88]).

Question 13

What do vertical datums help to establish (2)?

Answer 13

1. Elevation; and

2. Bathymetry

Question 14

Why is it important that maps use the same Datum?

Answer 14

Layers might not match up and create discrepancies (e.g., a difference of a few meters could spell disaster for building erected in flood planes).

Question 15

What’s involved in georeferencing? What can you do afterwards? Provide an example.

Answer 15

1. Georeferencing may involve shifting, rotating, scaling, skewing, warping, or orthorectifying data.
2. Once all data is calibrated to one geographic referencing system, it can be viewed, queried, and analyzed with other geographic data.
3. An example might be adjusting a raster images so that it is correctly positioned onto the geographic features of vector files which are already correctly placed.