Introduction to Coordinate Systems Flashcards
X values
Longitude
Y values
Latitude
What is the Earth’s shape?
Oblate Ellipsoid
Earth rotates on what axis?
Shortest axis, minor axis
Equator is what kind of axis?
Major axis
Earth’s shape is ellipsoid, what other term is also used? Most map project authorities consider both terms correct.
Spheroid
Satellite technology has revealed several elliptical deviations on the earth. The south pole example?
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.
Name two common spheroids for North America?
1) Clarke 1866 spheroid and
2) GRS80 spheroid is replacing Clarke 1866
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)
Spheroids
Differences in spheroids are not noticeable at scales smaller than what?
1:5,000,000
Every GIS requires at least one _______ system
Coordinate
Two types of coordinate systems used in a GIS?
Geographic coordinate systems and projected coordinate systems
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.
Geographic coordinate system
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.
Projected coordinate system
True/False: A geographic coordinate system identifies location on a globe using angular degrees rather than linear measurements.
True
At which scale do differences in spheroids generally become visible?
1:5,000,000
True/False: No matter which coordinate system you use, a specific location on the earth will have the same coordinates.
False
True/False: When a more accurate spheroid has been produced, all spatial geodatabases are updated to use the new spheroid.
False
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 (_______) and longitude (______) called a _______.
latitude - Parallels
longitude - meridians
graticule
Latitude lines are _________ and run parallel to the _______. Longitude lines are ________ lines that converge at the _________. Combining the latitude and longitude lines creates a _________.
horizontal, equator.
vertical, earth’s poles
graticule
Four primary components of each geographic coordinate system?
Angular units of measure
Prime meridian
Spheroid
Datum
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.
Angular units of measure
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.
Prime meridian (all blanks)
A _______ is the mathematical model that estimates the size and shape of the earth.
Speroid
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.
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.
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?
Geographic coordinate systems
T/F - Coordinate information can be stored as values in a table
True
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.
False
To create a map to compare global data, which type of spatial reference should be used?
Earth-centered datum
Three different Projection Types?
Cylindrical Projection
Conic Projections
Azimuthal/Planar Projections
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.
Cylindrical Projection
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.
Conic Projections
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.
Azimuthal/Planar Projections
Which Projection to use? For map areas that extend north–south
use a cylindrical projection
Which Projection to use? For map areas that extend east–west
use a conic projection
Which Projection to use? For map areas that have equal extent in all directions
use an azimuthal projection
Every projection type causes distortion in a minimum of two map properties. What are the four map properties?
Shape, area, distance, or direction
What Projections preserve shape but not area?
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.
What projections preserve area but not shape?
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.
What projections preserve true scale between one or two points to every other point on the map, or along every meridian?
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.
What projections preserve direction from one or two points to every other point?
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.
What projections preserve the shortest route (distance and direction) but cannot preserve area?
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.
What projections try to balance shape and area distortion?
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.
If a map preserves two spatial properties, one of them is always what?
Direction
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?
Compromise
T/F. Projections cause distortion in a minimum of two of the following spatial properties: area, direction, distance, or shape.
True
To create a map for measuring how much total land is part of a national park, which spatial property should be preserved?
Area
Three surfaces are developable surfaces for creating map projections?
Cone, Plane, Cylinder
