Projections Coordinate Systems , Cartography Flashcards
What is geodetic datum ?
It’s a reference system that defines points on the earths surface using a model of the earths shape to establish a coordinate system for correct position measurement.
What is a coordinate system ?
It’s a framework that determines how locations are represented on a map. It provides a standardized method to reference and integrate spatial data ensuring accurate spatial relationships between features .
Key components of a coordinate system
Measurement framework : how coordinates are measured.( could either be
geographical coordinate system (GCS): using spherical coordinates measured from the earths center , is 3D
Or
Projected( projects earth coordinates onto a flat 2D surface)eg : Universal transmercator (UTM), Albert equal area or Robinson
Units of measurement :
projected coordinate: feets or meters
Geographic coordinates: decimal degrees.
What is map project definition
This is anothe component of coordinate systems in projected coordinate systems is describes how the 3D is converted to 2D.
A GCS geographical coordinate system is often called what ?
A datum , which partially incorrect because a datum is one part of a GCS
What do the spheroid and datum do in a GCS?
Spheroid : defines the size and shape of the earth model
Datum : connects the spheroid to the earths surface.
What is a point referenced with in a GCS?
By it latitude and longitude values . Longitude and latitude are angles measured from the earths center to a point.
Projected coordinate system (PCS)
2D,
Has constant lengths, angles and areas across the 2 dimensions unlike GCS.
Always based on aGCS which is based on a spheroid.
Ipcontains map projection : a set of project parameters that customize a map for a specific location.
What is projection
The methods of representing the surface of a sphere onto a plane
True or false: all map projections show a distorted representation of earth
True
True or false: different map projectspions exist in order to preserve some properties of the sphere (area , shape direction, bearing , distance and or scale .)
True
What are projection characteristics?
Position of light source (check post it)(central,orthographic,stenographic)
Type of model( azimuthal,cylindrical,conic)
Orientation of projection surface (check posit )(normal, transverse, oblique )
What are tangent and secant cases in projections
These describe how project surfaces ( like cone or cylinder )interact with the earth’s surface.
Tangent : the projection surface touches the earth at a single point or along A line.
Secant : the projection surface cuts through the earth, intersecting along two lines .
Some common projection examples
- Mercator & transverse Mercator :UTM , SWEREF,RT90.
- EQUAL AREA PROJECTIONS : Hammer-aitoff, cylindrical equal area
Balance of shape and scale : miller cylindrical , Aitoff.
What is the difference between Geodesic( great circle ) and loxodrome ( rhumbline )Geodesic
Geodesic : this is the shortes pt distance between two points on a sphere
Loxodrome: this is a path that maintains a constant bearing crossing all meridians at the same angle . Easier for navigation as compass is steady , but isn’t the shortest route .
Mercator map
True directions from one point to the other maintaining shape of all features.
Cannot show poles
U
T
M
Usually used for large scale within a certain UTM zone.
Projection is formed using a transverse cylindrical projection.
Divides the earth into pole to pole zones along 6 degrees of longitude wide.
True or false U TM is not normally used above 80 degrees north or south
True
