Introduction to Coordinate Systems Flashcards
Use ArcGIS Pro to explore coordinate system basics and describe the effects on GIS data resulting from transforming coordinates on a 3D surface to a 2D surface.
What are coordinate systems?
Made up of x, y, and z coordinates, described with meridians, the equator, and latitude and longitude lines
What is the shape of the Earth?
Oblate Ellipsoid
What are the two most common spheroids in North America?
GRS80 (more accurate) and Clarke 1866 (most widely used)
What are geographic coordinate systems (GCS)?
They use a 3D spherical model. Use coordinate values to identify a feature on a map using latitude and longitude.
What are projected coordinate systems (PCS)?
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.
Describe latitude
Lines that run East and West parallel to the equator.
Describe longitude
Lines that run North and South; they converge at the poles.
What are the four components of a GCS?
Angular Units of Measure, Prime Meridian, Spheroid, Datum
Components of a GCS
Angular units of measure are…
relative to the center of the Earth.
Components of a GCS
The two characteristics of the Prime Meridian are…
0 degrees longitude and the official meridian is located in Greenwich, England.
Components of a GCS
What is a spheroid?
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.
Components of a GCS
What is a datum?
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.
What are the three most common North American Datums?
NAD1927, NAD1983, and WGS1984
What are the three projection types?
Cylindrical, Conic, and Azimuthal/Planar
Describe cylindrical projections.
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.
Describe conic projections.
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.
Describe azimuthal/planar projections.
These are centered on the poles. Longitudinal lines radiate outward and latitudinal lines appear as concentric circles.
This type of projection should be used for areas that extend North and South. This is also typically used to map the tropical regions.
Cylindrical
This type of projection should be used for areas that extend East and West. This is also typically used to map the middle latitudes.
Conic
This type of projection should be used for areas that have equal extent in all directions. Use this projection to map the polar regions.
Azimuthal/Planar
What are the four properties in which an area can be distorted?
shape, area, distance, and direction
If a map preserves two spatial properties, one of them will always be what property?
Direction
Describe the Conformal distortion
Preserves shape, not area
Describe the Equal Area distortion
Preserves area, not shape
Describe the Equidistant distortion
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
Describe the Azimuthal distortion
Preserves direction from one or two points to every other point, not shape or area
Describe the Gnomonic distortion
Preserves the shortest route (distance and direction), not area
Describe the Compromise distortion
Try to balance shape and area, not one property is completely accurate but no property is extremely inaccurate.
