An important consideration in
mapping our world
onto a two
Define the spatial
on Earth and their
on a map.
Why project data?
Data often comes in geographic, or spherical
coordinates (latitude and longitude) and
cannot be used for area calculations.
Some projections work better for different
parts of the globe giving more accurate
“All maps lie flat, therefore all
Issues and Limitations
Map projections are attempts to portray the surface
of the Earth or a portion of the Earth on a flat
Some distortions of different types always result
from this process.
Some projections minimize distortions in some of
these properties at the expense of maximizing errors
Some projections are attempts to only moderately
distort all of these properties.
Thus, the best projection depends
upon the use of the map.
Choosing a Map Projection
• which region to display (e.g. world, north pole,
• Resolution of the region
• Geometric properties of the region
• Purpose of using maps
such that distortion can be minimized
When the scale of a map at any point is the same in any
direction, the projection is conformal. Meridians (lines of
longitude) and parallels (lines of latitude) intersect at
right angles. Shape is preserved locally.
A map is equidistant when its distance from a single
location to all other locations are preserved.
A map preserves directions when it is azimuthal, when
direction from a single location to all other locations are
It is the relationship between a distance portrayed
on a map and the same distance on the Earth.
When a map portrays areas over the entire map so
that all mapped areas have the same proportional
relationship to the areas on the Earth that they
represent, the map is an equal –area map.
Aspects of the Projection
The aspect describes how the developable
surface is placed relative to the globe. It may be;
normal -such that the surface's axis of symmetry
coincides with the Earth's axis
transverse -at right angles to the Earth's axis
or oblique -any angle in between
• The developable surface may also be either;
tangent -means the surface touches but does
not slice through the globe;
secant -means the surface does slice through
Projections can be conceptually created by
projecting from one geometric shape (a
sphere) onto another (a cone, cylinder, or
Good for displaying the
Globe is projected onto a
cylinder tangent at
Low distortion at equator
A good choice for use in
equatorial and tropical
regions, e.g., Ecuador,
Example of a Cylindrical Projection:
Invented by Gerhardus
Cartographer- in 1569
A special purpose
projection, intended as a
It is conformal,
azimuthal, and has true
scale around equator.
Problems with Mercator
Preserves shape (a
conformal type) but
Used by John Birch
Society in Cold War to
show “Red Menace”
Africa, in reality is 14X
larger than Greenland in
Poles cannot be shown
Good for displaying mid- latitude area such as U.S.
Surface of globe projected onto cone is tangent at
Distorts N & S of standard parallel(s)
Normally shows just one semi hemisphere in middle
Lambert Conformal Conic is a widely used
Planar or Polar Projection
Good for displaying hemisphere
with one focus.
Surface of globe is projected
onto a plane tangent at only one
point (frequently N or S pole).
Works well in highlighting an
Shows true bearing and distance
to other points from center or
point of tangency.
Also called “football” projection
Tend to be equal- area
Not bad for world maps
Example: Mollweide Projection
Goode’s Homosoline Interrupted
Good for climate, soils, landcover – latitude and
Mild distortion of shapes
Interrupts areas- oceans, Greenland
Thank you for listening!
Chelsea P. del Rosario
Julian Philipp A. Soriano
Shaina Mavreen Villaroza