Introduction to Coordinate Systems

Question 1

X values

Answer 1

Longitude

Question 2

Y values

Answer 2

Latitude

Question 3

What is the Earth’s shape?

Answer 3

Oblate Ellipsoid

Question 4

Earth rotates on what axis?

Answer 4

Shortest axis, minor axis

Question 5

Equator is what kind of axis?

Answer 5

Major axis

Question 6

Earth’s shape is ellipsoid, what other term is also used? Most map project authorities consider both terms correct.

Answer 6

Spheroid

Question 7

Satellite technology has revealed several elliptical deviations on the earth. The south pole example?

Answer 7

The most southerly point on the minor axis, is closer to the major axis (the equator) than is the north pole, the most northerly point on the minor axis.

Question 8

Name two common spheroids for North America?

Answer 8

1) Clarke 1866 spheroid and
2) GRS80 spheroid is replacing Clarke 1866

Question 9

Remember that changing ________ changes the location values for the features that you are mapping. Because of the complexity of changing ________, ground-measured ___________ will remain in use for several years. (same word for all blanks)

Answer 9

Spheroids

Question 10

Differences in spheroids are not noticeable at scales smaller than what?

Answer 10

1:5,000,000

Question 11

Every GIS requires at least one _______ system

Answer 11

Coordinate

Question 12

Two types of coordinate systems used in a GIS?

Answer 12

Geographic coordinate systems and projected coordinate systems

Question 13

A ________ uses a three-dimensional spherical model to identify points or areas on the surface of the earth. The pairs of coordinate values that identify a feature on a map are relative to its geographic coordinate system. Each coordinate system is commonly illustrated with a network of intersecting lines of latitude (parallels) and longitude (meridians) called the graticule.

Answer 13

Geographic coordinate system

Question 14

A _______ is based on a geographic coordinate system. They are used to convert feature locations from the spherical earth to a flat map. To do so, latitude and longitude coordinates from geographic coordinate systems are projected to planar coordinates.

Answer 14

Projected coordinate system

Question 15

True/False: A geographic coordinate system identifies location on a globe using angular degrees rather than linear measurements.

Answer 15

True

Question 16

At which scale do differences in spheroids generally become visible?

Answer 16

1:5,000,000

Question 17

True/False: No matter which coordinate system you use, a specific location on the earth will have the same coordinates.

Answer 17

False

Question 18

True/False: When a more accurate spheroid has been produced, all spatial geodatabases are updated to use the new spheroid.

Answer 18

False

Question 19

Uses a three-dimensional spherical model to identify points or areas on the surface of the earth. The pairs of coordinate values that identify a feature on a map are relative to its _______?

Answer 19

Geographic coordinate system

Question 20

Each coordinate system is commonly illustrated with a network of intersecting lines of Latitude (_______) and longitude (______) called a _______.

Answer 20

latitude - Parallels
longitude - meridians
graticule

Question 21

Latitude lines are _________ and run parallel to the _______. Longitude lines are ________ lines that converge at the _________. Combining the latitude and longitude lines creates a _________.

Answer 21

horizontal, equator.
vertical, earth’s poles
graticule

Question 22

Four primary components of each geographic coordinate system?

Answer 22

Angular units of measure
Prime meridian
Spheroid
Datum

Question 23

The graticule of latitude and longitude lines is an angular measurement system. All features on the earth’s surface are located using measurements that are relative to the center of the earth.

Answer 23

Angular units of measure

Question 24

A _______ is the zero value for longitude. While the official ________ passes through Greenwich in southeast London, United Kingdom, the choice of _________ for a given coordinate system is somewhat arbitrary. It is not necessary to define a zero value for latitude because it is always the equator.

Answer 24

Prime meridian (all blanks)

Question 25

A _______ is the mathematical model that estimates the size and shape of the earth.

Answer 25

Speroid

Question 26

A _______ provides a frame of reference for measuring locations on the surface of the earth. It defines the origin and orientation of latitude and longitude lines.

Answer 26

Datum While a spheroid approximates the shape of the earth, a datum defines the position of the spheroid relative to the center of the earth. The underlying datum and spheroid to which coordinates for a dataset are referenced can change the coordinate values.

Question 27

What is represented by a graticule of intersecting parallels (latitude) and meridians (longitude), uses a three-dimensional spherical model to identify specific locations on the earth, and coordinates are based on latitude and longitude values?

Answer 27

Geographic coordinate systems

Question 28

T/F - Coordinate information can be stored as values in a table

Answer 28

True

Question 29

T/F - If you cannot find the original projection for geographic data, you can use any geographic coordinate system that is appropriate for the region of the world that you are mapping.

Answer 29

False

Question 30

To create a map to compare global data, which type of spatial reference should be used?

Answer 30

Earth-centered datum

Question 31

Three different Projection Types?

Answer 31

Cylindrical Projection Conic Projections Azimuthal/Planar Projections

Question 32

Type of projections are created by wrapping a cylinder around a globe and projecting light through the globe onto the cylinder. They represent meridians as straight, evenly spaced, vertical lines; they represent parallels as straight, horizontal lines. Meridians and parallels intersect at right angles, as they do on the globe.

Answer 32

Cylindrical Projection

Question 33

Type of projections are created by setting a cone over a globe and projecting light from the center of the globe onto the cone. The simplest contacts the globe along a single latitude line called the standard parallel. In general, distortion increases north and south of the standard parallel.

Answer 33

Conic Projections

Question 34

Type of projection, project map data onto a flat surface. When that point is either the north or south poles, longitude lines radiate outward from the pole at their true angle. Latitude lines appear as a series of concentric circles. They are used most often to map the polar regions.

Answer 34

Azimuthal/Planar Projections

Question 35

Which Projection to use? For map areas that extend north–south

Answer 35

use a cylindrical projection

Question 36

Which Projection to use? For map areas that extend east–west

Answer 36

use a conic projection

Question 37

Which Projection to use? For map areas that have equal extent in all directions

Answer 37

use an azimuthal projection

Question 38

Every projection type causes distortion in a minimum of two map properties. What are the four map properties?

Answer 38

Shape, area, distance, or direction

Question 39

What Projections preserve shape but not area?

Answer 39

Conformal projections. In this example, the Mercator projection is conformal in that angles and shapes within any small area are fairly accurately depicted. All the continents are the right shape, but Greenland looks disproportionally large, and Africa looks small.

Question 40

What projections preserve area but not shape?

Answer 40

Equal-area projections. This example, the sinusoidal projection, is an easily plotted equal-area projection for world maps. Here, Greenland looks like the right size in comparison to other land masses, but North America and Australia are the wrong shape.

Question 41

What projections preserve true scale between one or two points to every other point on the map, or along every meridian?

Answer 41

Equidistant projections. In this example, showing the equidistant conic projection, distances along all meridians are proportionally correct. Distortion is constant along any given parallel, while distances are correct and free of any distortion along the standard parallels. Additionally, there is no shape, area, or scale distortion along the standard parallels, however the further away from these standard parallels, the greater the distortion.

Question 42

What projections preserve direction from one or two points to every other point?

Answer 42

Azimuthal projections. For this example, the azimuthal equidistant projection, distances and directions to all places are true only from the center point of the projection. Any distance or direction measured from the center of the map will be accurate, but any distance or direction measured from any other point will be inaccurate.

Question 43

What projections preserve the shortest route (distance and direction) but cannot preserve area?

Answer 43

Gnomonic projections. With this example, the north pole gnomonic projection, any straight line drawn on the map is on a great circle, but directions are true only from the center point of projection.

Question 44

What projections try to balance shape and area distortion?

Answer 44

Compromise projections. No flat map can be both equal area and conformal; you need a globe for that instance. One widely used example is the Winkel Tripel projection, which minimizes overall distortion but does not preserve any of the four spatial properties. Compromise projections are named because no one property is completely accurate, but no property is extremely inaccurate.

Question 45

If a map preserves two spatial properties, one of them is always what?

Answer 45

Direction

Question 46

To create a map that has minimal distortion but does not perfectly preserve any of the four spatial properties, which type of projection should be used?

Answer 46

Compromise

Question 47

T/F. Projections cause distortion in a minimum of two of the following spatial properties: area, direction, distance, or shape.

Answer 47

True

Question 48

To create a map for measuring how much total land is part of a national park, which spatial property should be preserved?

Answer 48

Area

Question 49

Three surfaces are developable surfaces for creating map projections?

Answer 49

Cone, Plane, Cylinder