Creating a Flat Earth Image Flashcards
What is the difference between graticule and grid
Graticule Latitude and longitude is an example. For grid X/Y coordinates is an example.
Transverse
Rotated cyclindar 90 degrees
Developable Surface:
A geometric shape such as a cone, or cylinder, that can be flattened without being distorted. Many map projections are classified in terms of these shapes.
Cylindrical Projection
Cylindrical projections result from projecting a spherical surface onto a cylinder. Can be tangent or secant. A secant cylindrical projection has 2 lines of intersection between the cylinder and the globe both are small circles. When the cylinder is tangent to the sphere contact is along a great circle (the circle formed on the surface of the earth by a plane passing through the center of the earth. Cylinder is a good projection for wanting all of earth! The end result is a rectangular map!
Conic Projection
Conic projections result from projecting a spherical surface onto a cone. When the cone is tangent to the sphere, contact is along a small circle. In the secant case the cone touches the sphere along 2 lines, one great circle and the other a small circle. Not a good projection if wanting to map all of earth. Great for one of the poles.
Planar Projection:
Results from projecting a spherical surface onto a plane. When the plane is tangent to the sphere contact is at a single point on the surface of the earth. In the secant case the plane touches the sphere along a small circle if the plane does not pass through the center of the earth when it will touch along a great circle.
Line of Tangency
When a developed surface comes into contact with the globes surface along a single line the projection is considered to be tangent. (the projection surface is tangent to the globes along that line).
Line of Secancy
When a developed surface comes into contact with the globes surface along 2 lines, the projection is considered to be secant! ( the surface cuts through the surface of the globe)
Secant Cylindrical Projection:
the cylinder touches the sphere along 2 lines, both small circle (a circle formed on the sruface of the earth by a plane not passing through the center of the earth)
Tangent Cylindrical Projection:
Contact is along a great circle (the circle formed on the surface of the earth by a plane passing through the center of the earth)
What happens when the cylinder upon which the sphere is projected is at a right angle to the poles?
The cylinder and resulting projection is transverse! When the cylinder is at some other non-orthgonal angle with respect to the poles the cylinder and resulting projection is oblique.
When the cone is tangent to the sphere, contact is along what?
A small circle!
When the cone is secant to the sphere the cones touches the sphere along….
2 lines! one a great circle and the other a small circle.
In a planar projection what happens when the plane is tangent to the sphere?
The contact is at a single point on the surface of the earth.
In a planar projection what happens when the plane is secant to the sphere?
The plane touches the sphere along a small circle if the plane does not pass through the center of the earth, when it will touch along a great circle.
What are the different types of light sources?
- ) Orthographic: Infinite light source. A view of the world from a vetical perspective. As if you were looking at it at the entire earth from directly above the surface.
- ) Stereographic: Light source at antipode
- ) Gnomic: Light source at center of globe. Map projection with a theoretical
Equation for Scale Factor
Actual scale/Principal Scale= Scale Factor
Scale factor is used for
Understanding the amount of distortion on the map
Lambert Azimuthal Equal Area is a product of….
Planar surface
mercator projection is also a
cylindrical projection
If we move away from a standard line does distortion increase or decrease?
It increases!
What does a conformal map preserve?
Shape preservation
What does a Equidistant Map Preserve?
Distance
What does a Azimuthal Map Preserve?
Direction
What does an Equal Area Map Preserve?
Area
Can a map projection maintain scale everywhere?
NOPE
What does a Mercator Projection Preserve?
It is a conformal map so it maintains shape!
Lambert Conformal Conic projection, what does it preserve and distort?
Area and Shape are distorted away from standard parallels. Directions are true in limited areas.
What is the official projection of Canada?
Lambert Conformal Conic
Azimuthal equidistant projection what does it preserve and distort?
- Distances measured from the centre is true.
- Distortions of other properties increases as you move away from the center point!
- Sometimes used to show air-route directions.
In order to preserve area what happens as we get fartheraway from the standard line?
compresses
Where is the only place you can preserve shape and area?
The standard line, the standard point or standard lines!
Secant Planar has a
single standard line.
Tissot’s Indatrix:
Equal area map. Represents circles of distortions with the intersection of long and lat. We apply to those circle the distortion that that area is experiencing.
Why would we want to use the mercator projection?
If mapping the equator! Because the equator is the standard line where there is no distortion.
What geographic considerations might contribute to projection selection?
- Shape of area
- Extent of area
- Critical features
- Region or area of the earth.
Principal Scale:
(scale of a globe radius to atual earth radiues). scale of the model of earth being used for a map to the earth. Principal scale and actual scale will be the same all over the reference globe.
Actual scale:
The scale at any point on a maps surfacr in relation to the earth.
