GEOG 563: GIS
Map Projections
Map Scale
Geographic Coordinate Systems
Sphere
Flat Map
Map
Projection
Map Projections
A projection is a
mathematical means
that
transforms
information from the Earth’s curved surface to a two-
dimensional medium—paper or a computer screen
Transforming a globe surface to a flat surface
always
results in distortion (e.g.,
area
,
distance
,
direction
,
and
shape
—ADDS)
Move from 3D to 2D
Cannot preserve all properties.
Both areas and angles are distorted
The simplest projection – “
Geographic Projection”
- simply uses latitude and longitude as “2-D” coordinates
(although they are actually defined on a 3D globe)
Map Projections
Classification of Projections
Cylindrical
Projections
Conical
Projections
Planar or
Azimuthal
Projections
Example – Cylindrical
Example – Conical
Example – Planar
Classification of Map Projections
Disposition of the projection plane
Secant
– cut through the earth
Tangent
– lie flat at a tangent to some point on the globe
Standard Point/Line(s)
Standard point
Standard line(s)
Standard parallels
Measures are most accurate
where the projection surface
touches the sphere, i.e., at
the standard line(s).
Classification of Map Projections
Aspect
(
How the earth is viewed when it is projected
)
Normal (Equatorial):
standard point is on the equator or standard lines
are parallels
Transverse (Polar):
standard point is on north/south pole or
standard lines are parallel to meridians
Oblique:
none of the above
Distortions in a map projection
Areas
If a projection preserves area, it is called an
equal-
area
projections
Shapes
If a projection preserves shape (and thus angels), it
is called
conformal
projections
Distances
If a projection preserves distance, it is called an
equal-distance
projection.
Directions
Conformal Map Projections
Preserves Shape
No projection can provide correct shapes for large areas
Conformal projections - Show accurate shapes for
small
areas
by preserving correct angular relationships (directions)
Parallels and meridians intersect at
right angles
, as they do
on the globe, but the size is distorted
A map
CANNOT
be both equivalent and conformal.
Examples:
Mercator
Lambert conformal conic
Mercator projection
It preserves
shapes (angles),
i.e., it is a
conformal
projection
.
It distorts
Areas
Distances
…
Lambert Conformal Conic projection
It preserves angles (you
can simply tell from its
name)
It is used for mapping
countries and regions of
primarily east-west
extent (such as the U.S.
and Russia).
It is also used as the
basis of the U.S. State
Plane Coordinate
System (which you will
learn later)
Lambert
Conformal Conic
projection
Equal-Area Projections
Preserves Area (size)
Equivalent or equal-area
Represent the area of regions is correct or constant
proportion to earth reality
