Chapter 2 GeoSpatial Flashcards
(32 cards)
What is a geoid?
Model of Earth’s shape using mean sea level as a base and it takes mountains and trenches
What is an ellipsoid?
A model of the rounded shape of Earth
What is a datum?
An ellipsoid model that approx. the shape of Earth to enable accurate position, length, and area. Used for plotting locations
What is the relationship between geoid, ellipsoid and datum? What are the differences between them?
The relationship between them is that they all model the shape of the Earth.
The differences is that geoid takes mountains and trenches. Ellipsoid is a rounded shape. Datum is a reference surface of Earth
Why are there hundreds of datums in use? Why shouldn’t we just use one datum for all different places on Earth?
Different local ellipsoids of varying position and orientation had to be adopted to provide a best fit of the local mean sea level in different countries or regions.
Why does a datum have to be determined before using a geographic coordinate system?
A datum provides a frame of reference for measuring locations on the surface of the earth.
What are the differences between NAD83 and WGS84 datum
NAD83: reference to surface of Earth/datum for US and North America Continent
WGS84: a generalize model for the whole planet
Which datum should be used for the
globe? Which datum should we use for the United States?
For globe: WGS84
For US: NAD83
Which datum do most digital maps (e.g.,
Google Earth Pro, Google Maps, Bing Maps, etc.) use?
WGS84
What is a datum transformation? In what situation a datum transformation is required?
The process of changing measurements from one datum to measurements in another datum.
It is required for updated datums (Ex NAD27 to NAD83)
What is GCS?
Geographic Coordinate System is a global reference system to degerming the exact position of a point on Earth
What is latitude?
Parallels/ run in east to west direction of the Prime Meridian
What is longitude?
Meridians/run north to south from the North Pole to the South Pole of the Equator
What is the Equator?
The line of latitude that runs around the center of the Earth Starting point of 0 for latitude
What is the Prime Meridian?
Line of longitude that runs through the Royal Observatory in Greenwich, England
Starting Point of 0 for longitude
What are the latitudes for the Equator?
0 degrees latitude
What are the latitudes for the Tropic of Cancer? What are the latitudes for the Tropic of Capricorn?
Tropic of Cancer: 23.5 degrees north
Tropic of Capricorn: 23.5 degrees south
What are the latitudes for the Arctic Circle? What are the latitudes for the Antarctic Circle?
Arctic Circle: 66.5 degrees north
Antarctic Circle: 66.5 degrees south
How to describe a location using latitude and longitude? Make sure to know the correct format for writing a GCS coordinate.
Latitude, then Longitude
(N then W)
How to convert a GCS coordinate from DMS to DD?
Step 1: Convert Sec to Min
2: Calculate total Min
3: Convert total min to Degree
4: calculate total Degree
5: Same for longitude
How many degrees of longitude does each time zone cover in theory? Why don’t time zones exactly follow the lines of longitude?
15 Degrees
As Earth rotates on its axis, it moves about 15 degrees every 60 minutes. After 24 hours, it has completed a full rotation of 360 degrees.
Where is the International Date Line located (longitude)? How many time zones does the United States cover (including Hawaii and Alaska)?
180 degrees longitude
Six Time Zones
What is a map projection? Why do we need a map projection?
Converting 3D Map to 2D map.
We need a map projection to give a graphical reference to map data
Why do map projections always have distortions?
Because you can’t display 3D surfaces perfectly in two dimensions
