Introduction to Coordinate Systems

Question 1

What are coordinate systems?

Answer 1

Made up of x, y, and z coordinates, described with meridians, the equator, and latitude and longitude lines

Question 2

What is the shape of the Earth?

Answer 2

Oblate Ellipsoid

Question 3

What are the two most common spheroids in North America?

Answer 3

GRS80 (more accurate) and Clarke 1866 (most widely used)

Question 4

What are geographic coordinate systems (GCS)?

Answer 4

They use a 3D spherical model. Use coordinate values to identify a feature on a map using latitude and longitude.

Question 5

What are projected coordinate systems (PCS)?

Answer 5

They’re based on GCS. They’re used to convert locations from the spherical form to a flat map. Latitude and longitude is converted to planar coordinates.

Question 6

Describe latitude

Answer 6

Lines that run East and West parallel to the equator.

Question 7

Describe longitude

Answer 7

Lines that run North and South; they converge at the poles.

Question 8

What are the four components of a GCS?

Answer 8

Angular Units of Measure, Prime Meridian, Spheroid, Datum

Question 9

Components of a GCS

Angular units of measure are…

Answer 9

relative to the center of the Earth.

Question 10

Components of a GCS

The two characteristics of the Prime Meridian are…

Answer 10

0 degrees longitude and the official meridian is located in Greenwich, England.

Question 11

Components of a GCS

What is a spheroid?

Answer 11

A mathematical model that estimates size and shape of the Earth. The semimajor is latitudinal and the semiminor is longitudinal. They’re used in a region where the region doesn’t necessarily fit another region.

Question 12

Components of a GCS

What is a datum?

Answer 12

It provides a frame of reference for measuring locations on the surface. It defines the position of the spheroid relative to the center of the earth. The underlying datum and spheroid to which coordinate for a dataset are references can change coordinate values.

Question 13

What are the three most common North American Datums?

Answer 13

NAD1927, NAD1983, and WGS1984

Question 14

What are the three projection types?

Answer 14

Cylindrical, Conic, and Azimuthal/Planar

Question 15

Describe cylindrical projections.

Answer 15

This projection is created by wrapping a cylinder around a globe. It represents meridians as straight, evenly spaced vertical lines and parallels as straight, horizontal lines.

Question 16

Describe conic projections.

Answer 16

These projections are created by setting a cone over a globe and projecting light from the center to the cone. It contacts the globe along a single latitude called the standard parallel. In this case, distortion increases north and south of the standard parallel.

Question 17

Describe azimuthal/planar projections.

Answer 17

These are centered on the poles. Longitudinal lines radiate outward and latitudinal lines appear as concentric circles.

Question 18

This type of projection should be used for areas that extend North and South. This is also typically used to map the tropical regions.

Answer 18

Cylindrical

Question 18

This type of projection should be used for areas that extend East and West. This is also typically used to map the middle latitudes.

Answer 18

Conic

Question 19

This type of projection should be used for areas that have equal extent in all directions. Use this projection to map the polar regions.

Answer 19

Azimuthal/Planar

Question 20

What are the four properties in which an area can be distorted?

Answer 20

shape, area, distance, and direction

Question 21

If a map preserves two spatial properties, one of them will always be what property?

Answer 21

Direction

Question 22

Describe the Conformal distortion

Answer 22

Preserves shape, not area

Question 23

Describe the Equal Area distortion

Answer 23

Preserves area, not shape

Question 24

Describe the Equidistant distortion

Answer 24

Preserves true scale or distance between one or two points to every other point on the map, or along every meridian, not shape or area

Question 25

Describe the Azimuthal distortion

Answer 25

Preserves direction from one or two points to every other point, not shape or area

Question 26

Describe the Gnomonic distortion

Answer 26

Preserves the shortest route (distance and direction), not area

Question 27

Describe the Compromise distortion

Answer 27

Try to balance shape and area, not one property is completely accurate but no property is extremely inaccurate.