A cylindrical projection can be imagined in its simplest form as a cylinder that has been wrapped around a globe at the equator. The points on the spherical grid are transferred to the cylinder which is then unfolded into a flat plane. The equator is the "normal aspect" or viewpoint for these projections. This family of projections are typically used to represent the entire world. When projected from the centre of the globe with the normal aspect, the typical grid appearance for cylindrical projections shows parallels and meridians forming straight perpendicular lines. The spacing varies depending on the type of cylindrical projection. |
General characteristics
Equirectangular projection
|
|
Mercator projection
|
|
Lambert's cylindrical equal-area projection
|
|
Gall's stereographic cylindrical projection
|
Oblique Mercator
Oblique Mercator projections are used to portray regions along
great circles. Distances are true along a great circle defined by
the tangent line formed by the sphere and the oblique cylinder,
elsewhere distance, shape, and areas are distorted. Once used to
map Landsat images (now replaced by the Space Oblique Mercator),
this projection is used for areas that are long, thin zones at a
diagonal with respect to north, such as Alaska State Plane
Zones.
Transverse Mercator
Transverse Mercator projections result from projecting the sphere
onto a cylinder tangent to a central meridian. Transverse Mercator
maps are often used to portray areas with larger north-south than
east-west extent. Distortion of scale, distance, direction and area
increase away from the central meridian. Many national grid systems
are based on the Transverse Mercator projection, such as the
British National Grid (BNG).
Universal Transverse Mercator
The UTM projection is used to define horizontal, positions
world-wide by dividing the surface of the Earth into 6 degree
zones, each mapped by the Transverse Mercator projection with a
central meridian in the center of the zone. UTM zone numbers
similarly to the Gauss-Krüger (GK) projection numbers
designate 6 degree longitudinal strips extending from 80 degrees
South latitude to 84 degrees North latitude. UTM zone characters
designate 8 degree (4 degree in GK) zones extending north and south
from the equator. UTM zone eastings are measured from the central
meridian (with a 500km false easting to insure positive
coordinates). Northings are measured from the equator (with a
10,000km false northing for positions south of the equator).
Suggestions are welcome
guszlev@ludens.elte.hu