Chapter 2 GeoSpatial

Question 1

What is a geoid?

Answer 1

Model of Earth’s shape using mean sea level as a base and it takes mountains and trenches

Question 2

What is an ellipsoid?

Answer 2

A model of the rounded shape of Earth

Question 3

What is a datum?

Answer 3

An ellipsoid model that approx. the shape of Earth to enable accurate position, length, and area. Used for plotting locations

Question 4

What is the relationship between geoid, ellipsoid and datum? What are the differences between them?

Answer 4

The relationship between them is that they all model the shape of the Earth.

The differences is that geoid takes mountains and trenches. Ellipsoid is a rounded shape. Datum is a reference surface of Earth

Question 5

Why are there hundreds of datums in use? Why shouldn’t we just use one datum for all different places on Earth?

Answer 5

Different local ellipsoids of varying position and orientation had to be adopted to provide a best fit of the local mean sea level in different countries or regions.

Question 6

Why does a datum have to be determined before using a geographic coordinate system?

Answer 6

A datum provides a frame of reference for measuring locations on the surface of the earth.

Question 7

What are the differences between NAD83 and WGS84 datum

Answer 7

NAD83: reference to surface of Earth/datum for US and North America Continent

WGS84: a generalize model for the whole planet

Question 8

Which datum should be used for the
globe? Which datum should we use for the United States?

Answer 8

For globe: WGS84
For US: NAD83

Question 9

Which datum do most digital maps (e.g.,
Google Earth Pro, Google Maps, Bing Maps, etc.) use?

Answer 9

WGS84

Question 10

What is a datum transformation? In what situation a datum transformation is required?

Answer 10

The process of changing measurements from one datum to measurements in another datum.

It is required for updated datums (Ex NAD27 to NAD83)

Question 11

What is GCS?

Answer 11

Geographic Coordinate System is a global reference system to degerming the exact position of a point on Earth

Question 12

What is latitude?

Answer 12

Parallels/ run in east to west direction of the Prime Meridian

Question 13

What is longitude?

Answer 13

Meridians/run north to south from the North Pole to the South Pole of the Equator

Question 14

What is the Equator?

Answer 14

The line of latitude that runs around the center of the Earth Starting point of 0 for latitude

Question 15

What is the Prime Meridian?

Answer 15

Line of longitude that runs through the Royal Observatory in Greenwich, England

Starting Point of 0 for longitude

Question 16

What are the latitudes for the Equator?

Answer 16

0 degrees latitude

Question 17

What are the latitudes for the Tropic of Cancer? What are the latitudes for the Tropic of Capricorn?

Answer 17

Tropic of Cancer: 23.5 degrees north
Tropic of Capricorn: 23.5 degrees south

Question 18

What are the latitudes for the Arctic Circle? What are the latitudes for the Antarctic Circle?

Answer 18

Arctic Circle: 66.5 degrees north
Antarctic Circle: 66.5 degrees south

Question 19

How to describe a location using latitude and longitude? Make sure to know the correct format for writing a GCS coordinate.

Answer 19

Latitude, then Longitude

(N then W)

Question 20

How to convert a GCS coordinate from DMS to DD?

Answer 20

Step 1: Convert Sec to Min
2: Calculate total Min
3: Convert total min to Degree
4: calculate total Degree
5: Same for longitude

Question 21

How many degrees of longitude does each time zone cover in theory? Why don’t time zones exactly follow the lines of longitude?

Answer 21

15 Degrees

As Earth rotates on its axis, it moves about 15 degrees every 60 minutes. After 24 hours, it has completed a full rotation of 360 degrees.

Question 22

Where is the International Date Line located (longitude)? How many time zones does the United States cover (including Hawaii and Alaska)?

Answer 22

180 degrees longitude

Six Time Zones

Question 23

What is a map projection? Why do we need a map projection?

Answer 23

Converting 3D Map to 2D map.

We need a map projection to give a graphical reference to map data

Question 24

Why do map projections always have distortions?

Answer 24

Because you can’t display 3D surfaces perfectly in two dimensions

Question 25

What are three major types of map projection?

Answer 25

Conical, Plane Projection, Cylindric

Question 26

What type of map projection is the Mercator projection? What property does the Mercator projection preserve and what is the distortion?

Answer 26

Cylindric

It preserves shape and distorts size

Question 27

What type of map projection is the Albers conic equal-area projection? What property does this
projection preserve and what is the distortion?

Answer 27

Conical

Preserves size Distorts shape

Question 28

What type of map projection is the Lambert equal-area projection? What property does this projection preserve and what is the distortion?

Answer 28

Plane

Preserves Scale at the center of projection
Distorts Shapes, directions, angles, and distances are generally distorted.

Question 29

Which map projection does the UTM coordinate system use? How many zones are in the UTM system and how many degrees of longitude does each zone cover?

Answer 29

Mercator/ Cylindric

60 zones and 6 degrees of longitude

Question 30

Understand how to describe a location using UTM easting and northing coordinates.

Answer 30

Zone, Easting, then Northing

Question 31

What is the SPCS coordinate system? Where is this system mainly used?

Answer 31

Grid based system for measuring and determine coordinates. Mainly used for US Data

Question 32

What are the similarities and
differences between UTM and SPCS grid systems?

Answer 32

Similarities: Requires you to specify a zone, an easting, and a northing

Differences: SPCS are formed by following state or county boundaries