Lecture 2: Coordinates

Question 1

What are the three shapes of the Earth?

Answer 1

Sphere, Geoid, Ellipsoid

Question 2

Describe a sphere

Answer 2

Simple but inaccurate(uses mass center of Earths sphere)

Question 3

Describe a Geoid

Answer 3

Most accurate model, is slightly irregular/lumpy b/c of density variations in the Earth’s crust (used for geodesy/physics)

Question 4

Describe an Ellipsoid

Answer 4

More accurate than sphere: slightly flatter at the poles w/a bulge in the middle (equator)

Question 5

What does equipotential mean?

Answer 5

Every point is at the same potential

Question 6

What is the equipotential point?

Answer 6

The surface of the Earth’s gravity field which best fits global mean level

Question 7

How is the Geoid shaped?

Answer 7

Over oceans, Geoid is flat (no currents, no waves). Over continents, is is calculated by gravity measurements

Question 8

What is topography?

Answer 8

The real Earth’s surface (hills, valleys, plains as we experience them

Question 9

What is a datum?

Answer 9

A starting point for measurement

Question 10

What is a horizontal datum?

Answer 10

Known point on the Earth’s surface used for measuring coordinates, distances, and directions

Question 11

What is a vertical datum?

Answer 11

Known point on the Earth’s surface used for measuring heights

Question 12

What is a regional datum?

Answer 12

A datum almost every country in the world has to ensure accurate measurements in different parts of the world

Question 13

What is a goal datum?

Answer 13

Earth centered datums that replace original datums w/a common/more accurate standard

Question 14

What is the goal for global datums?

Answer 14

To make one system for maps of the entire planet, based on the center of Earth’s rotations

Question 15

What is Elevation?

Answer 15

Most commonly referenced to Mean Sea Level (MSL)

Question 16

A height measurements accounts…

Answer 16

for the topography of the earth relative to MSL

Question 17

What does an Ellipsoid approximate?

Answer 17

The shape of the Earth

Question 18

What is a Geographic coordinate?

Answer 18

define locations directly on an ellipsoid

Question 19

What is a Cartesian coordinate?

Answer 19

define locations on a plane

Question 20

What is Latitude?

Answer 20

Specifies the north–south position of a point on the Earth’s surface (up - down)

Question 21

What’s is the range of angles for Latitude?

Answer 21

0° at the Equator to 90° North (+) or South (-) at the poles, parallel the equator

Question 22

What is Longitude?

Answer 22

0° at the Equator to 90° North (+) or South (-) at the poles.

Question 23

What’s is the range of angles for Longitude?

Answer 23

0° at the Prime Meridian to 180° East (+) or -1800 West (-)

Question 24

Where is the Prime Meridian?

Answer 24

Greenwich, England

Question 25

What are geographic coordinates?

Answer 25

The locations that Latitude and Longitude gives us, most universal way of defining locations

Question 26

What are Geographic Coordinates are often measured in?

Answer 26

• Degrees(°), minutes (’) and seconds (”) (DMS)

- Decimal degrees (DD), must distinguish between North, East (+) and South, West(-)

Question 27

What is the Graticule?

Answer 27

the arrangement of lines of latitude and longitude on a globe or map

Question 28

What is a Coordinate reference system?

Answer 28

the preferred terminology for describing how location is referenced in modern geospatial technologies

Question 29

What is a map projection?

Answer 29

Method for converting the earth’s curved surface to a map’s flat surface
➢Modern map projections are created using mathematical formulas
➢A map projection flattens the earth!

Question 30

Why do we need map projections?

Answer 30

Paper is flat

• Computer screens are flat
• Mobile devices are flat
• You can see the whole Earth
• Easier to measure distance on a plane
• You cannot fold or roll up a globe

Question 31

What are projected coordinates?

Answer 31

Locations are defined by an x, y coordinate on a grid

Question 32

Name 3 Common Coordinate Reference Systems

Answer 32

• Universal Transverse Mercator (UTM)
• State Plane Coordinate System
• Web Mercator